Many things. For one, I think she should seek therapy. She has been clearly bullied, and her anxiety made worse in school, yet it is a "wrong" choice to recommend therapy. Her trauma regarding her mothers death and resulting anxiety doesn't seem to me a thing that just "going along" with her will fix. Clear neuroses like abnormal titty-fixation & abandonment issues add to the feeling that she should be helped. The MC being a caring guardian (or whatever...) should act or be alarmed?
Everything combines to her seeming too young, yet acting disturbingly lewd. There are absolutely sweet moments, but I felt uneasy and put off.
Then there's the time she hogs on-screen. But this is mainly an issue because I wasn't into her. But it was an issue because it started to increase the irritation.
All of these are highly personal. For example I was completely put off by Hayley's Story after the reveal. Trauma may be too real for me.