Ado is a girl. Adeleine and Ado are the same person. Now that the ground work is out of the way, allow me to explain why these should-be-obvious factoids are, in factoid, true.
In Kirby's Dream Land 3, there is a painter by the name of Ado. This is the first appearance of the beret wearing artist who is much different than the ball cap sporting Paint Roller who, despite the name, does not paint. To set this illustrator apart from the previous even more, she's apparently human. That's a new one.
Now, people are often confused about whether this painter Ado is a boy or a girl. Here's the thing: you're supposed to be. Japan is pretty big into androgyny. There's a whole "Visual Kei" that is going around this time, in fact. I don't want to dig into social dissection, but there's something about confusing people as to your true gender that's big over there. Look at plenty of animés stretching back as far as G-Force/Gatchamon to one of the two Rockets in Pokémon: Legend of Thunder, who was seemlessly changed into a female rather than male character. I won't go into why they did that, now. Just know that they did. And let's not forget Power Rangers, which commonly changes the Yellow Ranger into a chick just to fill up more demographic requirements. Back on point, Ado's gender is meant to be a mystery. She's merely some painter child until the final end credits roll.
In the final sequence, she's clearly a girl. She has dress on. She draws herself with lashes and hearts. It may not seem like much, but this is the gust that knocks the indecisive fence-sitter from the perch. I know I'm borrowing the phrase from the wrong source here, but, at that age, little kids are pretty much all the same. Plus, dress. C'mon. Additionally, in the mangas for the game, there a part comparing Ado to Samus Aran of Metroid fame and how the two look quite different for both being human. Also in the mangas, she's a girl in a dress. That probably has more relavence.
But, now, the real reason that Ado is of the female persuassion is due to her inspiration. Ado is a real person, you see, and a woman at that. Mizumori Ado was the official illustrator, not shockingly, Kirby's Dream Land 3 and Kirby 64: The Crystal Shards. All of those charming drawings and doodles of the characters, many of which were made by the character at the end of the game. That's right, Ado re-drew in the game what she already painted in real life. You're mind has just been freaked!
So why is Ado thought to be a boy? There are several culprits, but I can't actually pin the blame on any definitive source. The boyish haircut is probably at the top of the list. Little girls are traditionally pictured with longer hair, braids, or some type of animal tail themed positioning. The short cut doesn't exactly scream "lady-like". The name could also be related to it as -o endings are traditionally linked with masculine object. Read up on your Latin, kids. The -a suffix is the typical feminine route. Ancient declintions aside, many people simply default to a biased gender opinion. Backtracking to Samus Aran, everyone assumed that was a guy until specifically told or shown otherwise. When I, and noticeable others too, am referring to an unknown individual, I default to use of masculine pronouns. Is that sexist? Probably! But, hey, I'm not gonna say "he or she" every time.
So, Ado, yeah, that's a dame. Remember this forever. There isn't even the slightest hint of argument on behalf of the other side. The character is only ever officially stated as being the fairer gender. I think, maybe, in a Nintendo Power or other type of strategy booklet that she could have been called a boy. Of course, those people don't know anything. They often get things wrong that pertain directly to the game play. At least, they did back in the '90s before the video market went completely insane.
Adeleine is up next. This pudgy painter appeared in the following game. She does exactly what Ado did, being possessed by Dark Matter and drawing up a troop of enemies to attack the hero. She even has the same red beret and gray skirt on. The rest of the appearance is rather different. Instead of a smock to keep her cloths clean, she wears a simply green sweater. The hair is a little different and darker. People see the visual differences and the name change to decide that skin deep is as far as they want to investigate the matter.
More background comparisons. Look at the enemy Chilly and how much he's changed over the years. His design literally flipped with his head width swapping with his body size. Sir Kibble, too, has worn many masks in his days, as well as alternate names (Lord Kibble). How about Meta Knight? All the slight improvements make him look almost completely new. There are others who experience this transformations, but the reason for it is always the same: graphics. When the way a sprite is generated is changed, the character design can be improved, too. Sometimes, the old design may just look silly in the new manner. Other times, more can be put in.
In the case of N64, a lot had to be removed. Jumping from sprites to three dimensional models for the first time, and so early in the 3D gaming era, is a challenge. Many enemies are barely recognizable if not for their notiriaty throughout the many titles. Can you honestly tell me that Whispy Woods looks anything like he use to? Truthfully, no, but the name is in tact. Ado didn't have this luck.
The name "Adeleine", really, isn't that different than Ado. It's no differant than if one were to be confused by you calling someone Douglas rather than just Doug. It's not obvious to us, but Adeleine's true name, when written in Japanese, is spelled out Adoreenu. It contains "Ado" right in it. So, the name is 50% that of the previous painter who exhibited the exact same ability. Additionally, with the crossing into 3D, early 3D which struggled to make clothing, especially flat things like aprons that clung close to the body. The skirts are all circular and away from the body, if you notice, as to not have to shift them for body movements.
What's the phrase? (I'll eventually get to every coloquialism, don't worry) "If it looks like a duck, sounds like a duck, and quacks like a duck"? Well, Adeleine looks as close as they were graphically able to get them, and judging from some of the other adaptations, it really was. Her name even contains the whole name of the former. Finally, they both do exactly the same thing -- paint and create. The battles are nearly identical in format. If people argue that Wiz and Paint Roller and linked together, they should have no trouble swallowing this pill.
Ado is Adeleine. Yes, you can revamp and update a character. Things aren't written in stone. They've changed the entire structure of Dream Land and layout of the galaxy. Adding some letters on the end of the name and smacking on a smock aren't far fetched. Maybe they felt that further distinction was needed between the person and the character. If she was a one-time appearance, then it wouldn't matter much, but if a second appearance was coming, and it was unknown if more would follow, Ado herself could have requested that some separation be added. A character should be able to stand up on its own to feet even if birthed and based on something or someone else.
This is far from the most outlandish thing Kirby fan have been expected to play along with. Remember when Meta Knight tried to take over Dream Land and then turned goody-goody in the next title he appeared in? Yep, still dragging up that dead horse. Ado is a girl, undoubtedly. Ado is Adeleine, obviously. A girl can wear other shirts. She can cut her hair. She can even have a pet or nick name. She's a person, after all, and not some naked, bald, round thing that looks identical to hundreds of other naked, bald, round things.
That being said, now shaddap 'bout it. The coffin is nailed and buried. Move along.