Lucy Taylor has been a good girl—but a good day still eludes her. Thanks to her sitter having to cancel on short notice, she is forced to spend all day with her parents at work. Fortunately, hope comes on angelic wings—literally! Karina, the older sister of a friend of Lucy's from school, swoops in to rescue her from yet another boring day by sitting for her the entire time! And unlike others that came before, the angel is able to provide the deep attention and helpful ear that the growing young lady always wanted.
https://archiveofourown.org/works/26736331/chapters/65227198

(Entirely SFW! It's just a fluffy cute friendship fic through and through. It's not MLP-related, but does include magical beings, so could be thought of as a bit Equestria Girls-y!)