More "personal interpretation," IMO. The stated qualities are brattiness, lack of self-esteem, and inexperience. Well, the latter applies at least equally to Lucy and Vicky, both of whom were virgins (I don't remember if Kitty was). I'd argue that the "lack of self-esteem" applies equally to Lucy, though it's expressed very differently. So the only one of the stated qualities (other than physical size) that applies exclusively to Sarah is "brattiness." Whether that justifies considering her "borderline loli" is, I guess, a matter of opinion.