SOLVED. Girl has gay dad and missing/dead older sister - YA realistic fiction [s]

[Spockles]

I read the physical book, probably sometime between 2005-2009ish. A teenage girl is dealing with her older sister being missing (I can't remember if they know she's dead at the beginning). The family (the girl, her mom, stepdad, stepbrother, too, maybe) go to family therapy. Her dad is gay and lives with his partner. There's a flashback to her sister and her visiting their dad secretly and meeting the partner, and the protagonist doesn't realize that he's gay. At some point a policewoman visits the girl's family regarding the missing/dead sister, and it's implied that the sister prostituted herself in defiance to prove she's not gay and that she was murdered by a lover.

If anyone could tell me the title, I'd greatly appreciate it!

[Valerie]

My first thought was Saving Zoë but I'm not sure that totally fits. It's been awhile since I read it.

[Spockles]

Sounds really similar, but looking at the shelves/reviews, not it. BUT looking at the previous suggestions in the discussion/solved topic about that book, I'm pretty sure I found it:Alison, Who Went Away.

Thanks for the suggestion!