Racecar Start, Jalopy Ending

This book took off like a shot for me, but as the story progressed, things definitely took a turn. I found the protagonist extremely sympathetic initially, only to end up really abhoring her. I felt her dramatic U-turn was implausible, which made her extreme actions then seem unlikely. The story is about an orphan who is taken in by an unlikely benefactress when all her other family can't be bothered. As tenuous as their initial relationship is, they eventually form a bond that seems to have possibilities. When her beloved, but morally questionable brother meets his sister's new guardian, however, things get more complicated. Love the beginning, but hated the end.