Well, I think that you're right in some ways- but at least they included Kiara in the Lion Guard, not like she wasn't in it. So yeah, I agree she is a bit more bratty but you know teen/adult Kiara is a bit bratty too in TLK2. And about her design, well the people changed Simba and Nala to their original movie colors, and even Nala looks weird. But hey, they can only do their best when it comes to redesigning characters to fit into their movie/show.
Though this is just my opinion. ^^

Scene continued:
Kiara: Do know what it's like knowing you have to be perfect all the time not to disappoint dad?
Kion looks around awkwardly: Well no but..
Kiara: You don't so don't judge me! I've had to say goodbye to my friends while you just get to hang out all day yours and still have it not matter to dad!
Kion: That's the problem what ever I do even if I try my best it's never as good aps yours!
Dad always love you more!
Kiara: Well your just to selfish to see when any one else hurts!
All you care about is you and that's all you'll ever care about!
Kiara runs away crying and Kion gasps but quickly covers it up and turns away angrily.
Kion: What does she know anyway?

I didn't like Kiara in the secound movie she seemed naive but I hate the later version of her. However, if Disney wants to give complexity to her that's great! I don't think they will though but if they did I'd be for the change. I agree Strawberybubble 456.
Example complex character scene:
Kiara: Hey Kion off playing with you friends? (Snicker with friends)
Kion: I'm not playing!
Friend of Kiara: Then what exactly are you doing?
Kiara: Yeah little brother what are you doing?
Kion: I'm..well..I'm..um..you see.. (Looks around and at paws)
Kiara: Yeah that's what I thought (snicker with friends)
Kion: Well so what! At least I'm happy!
Kiara and friends gasp
Friend of Kiara: Oh no you didn't!
Kion: What'd you got to say to that miss perfect? (Condesending)
Kiara begins crying
Kiara friends gasp
Kiara: Leave!
Kiara friends: Is that a good idea?
Kiara: Go!
Other Kiara friend: Yes! (Cubs look shocked Kion quickly hides it)
Kiara friends run away fast.

I don't like it either since kiara is one of my favorite lion king characters besides nala and sarabi personal I think kiara is secretly jealous of kion because he doesn't have to worry about the kingdom when he's older and he gets to play all day and she only acts like that because she doesn't want to admit she's jealous of him

I hate how they changed her personality she was young and cute in the 2nd movie I liked how she had to find herself basically the whole point of the movie and now she is just a brat which she is not at all it bothers me a lot they ruined the point of the 2nd movie.

Me too disgusts me that they changed the personality of Kiara!

Yeah, I have the same opinion too. It really bothers me she's so excited for being queen already! However, I don't like these kind of changes (Yeah, every time they make a new thing - like this or the second movie- they always change something), So I just made a theory. Maybe Kiara was just showing off in front of Kion? U know, everyone likes to show off about something great even he/she doesn't want that. Plus, in the movie, when she said she didn't want to be queen, it was the time of evening after all the thing with Kovu and Zira. So she was in a bad mood. So she may be said that because of being in a bad temper?