I think she should really ask herself if the content she's been spurting out lately is something she'd personally watch. Like, if one of YouTubers she follows, uploaded a vlog like one of hers, speaking in a baby voice/moaning about minute everyday things, would she watch and enjoy it?
If the answer is no, maybe she shouldn't be putting the content out to the world to see.
I think Katie's figure was similar when she was a little smaller, it's just that Katie is so tiny height-wise, any little weight she might have put on, will show more. Plus I suppose, if her sister practices belly dance every day, and the most exercise Katie had lately, was trying some old shoes on, Becky will have a nicer figure.
Looks wise, I think because Becky is more or less sticking with her natural hair colour, she looks more striking. I like that she is enhancing her curly hair as well. I think Katie's hair naturally has a nice wave to it and that if she tried using the right products, it could look really cool.