Kitty > Chuck
Look at them being friends! While Kitty has never disliked Chuck (she isn't Lacus!) and has been extra protective if anything because of Ton she never really saw herself bonding with her. She doesn't really think they have much in common, but she'd be wrong. In fact, the reason they butt heads is likely because they have too much in common.
Chuck was busy being dead through the time Kitty was there for her most, but Chuck just standing with her as she left that party was huge. She doesn't even really realize the hugeness, but she feels it. She knows there was a big shift there even if they were on friendly enough terms leading up to it. She's a much better person to have on your side than against you. Though she also worries about her yelling at people who could really be dangerous (see also their fight regarding Tyki). She wasn't allowing Chuck enough agency out of protectiveness. And been there, done him-ness.