My friend's stepdad molested her?

Okay, normally I feel like I have an answer for everything. I'm lost here:

My best friend (uh, let's call her Megan) - Megan's parents got divorced when she was like eight or nine. And I guess her stepdad moved in with her mom (her dad had to move out of state for work) like a few months after. I don't know, it was pretty soon. They eventually got married and had a daughter (I'll call her Sally) who is now three.

Anyway, so Megan's dad moved back in state pretty quickly and did visitation stuff. Meanwhile, her stepdad (I've never liked him; she always used to talk about how he would call her mom if she took "too long" dropping Megan and her siblings off, just generally controlling) I guess became sort of like a second dad to her. And she just told me recently (we're nearly sixteen now) that he started molesting her during "backrubs" when she was like twelve. (I had no idea) she said that it happened alot, and that when it was happening it was like she was looking on, and knew that if she did something, told him to stop, etc, that it would "make it real". She said it took her like a year of telling herself nothing happened before it started eating away at her, and she started cutting (like eighth grade).

I guess during that time she became really depressed and disrespectful to her mom, so she sent her to live with her dad. Then she told me that it took her like another year to finally tell her mom, and her mom flipped. At Megan. Like she called her a liar and said she didn't believe her and all kinds of ****. I feel so terrible, because I didn't even realize anything was happening. She said she would have offed herself if it wasn't for Sally still being there.

Apparently her stepdad had other kids, daughters, that he didn't molest. He didn't molest Megan's little sister either (but her sister is younger and less developed than Megan). She said that she didn't think he would hurt Sally, like she was 90% sure, but you can never know.

So she called CPS in February, and they did an "investigation". You would think that the fact that her stepdad grabbed her *** in front of her mom once or that he's eighteen years older than her mom would be evidence in itself, but CPS dismissed it as lack of evidence, and recommended Megan get a shrink. So she did, and the shrink stuck her in a hospital for a week, and now that she's finally telling me she said she doesn't want to die (she wants to be a writer) but that sometimes her situation seems so hopeless because there's nothing she can do for her baby sister, and no immediate way out.

She keeps telling me that she has to do something, because if you're not part of the solution, you're part of the problem. But she can't sue for custody when she's eighteen, because she has no real proof against her stepdad. Her mom doesn't believe her - she thinks she had errotic dreams about her stepdad, of all people. Her dad doesn't believe her, either. She said that her thirteen year old sister told her that she was responsible for single handedly ruining her life (by tellling about her stepdad) and her brothers are younger and don't know, and then there's Sally and she's worried something's going to happen to Sally, and I just don't know what to tell her.

I mean what is she supposed to do? She wants to file a police report, but there's no evidence. I'm the only person outside of like doctors and her parents and CPS that she's told, and I just feel awful. I feel so bad for never noticing anything was wrong with her, even if she is like amazing at hiding her emotions. But I don't know how to help her situation. She keeps telling me that she just wants to get away and never talk to any of them again, but she can't because of Sally. She's really smart and an amazing writer and musician and I trust her not to kill herself. But how horrible to go through high school dealing with that! Does anyone have any ideas? Anything that could help her? Thank you.