I also think the abuse is largely behind this. She is screaming for help. I know it is SO hard as a parent.
Please do not whomp her. It will not help. Have you checked the local domestic violence shelter? they WILL have help, it is FREE (I have not heard of one where it isn't), and they can address the molestation and other issues.
You can set up payment arrangements with many hospitals. been there done that, on a LOT of occasions. Is there a university nearby? They may have a counselling center (where grad students do the counselling, very closely supervised) on a sliding scale fee.
As to her father, I do not know what to say. He sounds like a jerk, and his behavior is abusive, in my humble opinion.
Is there a Parents Resource Center in your town? They often work like a DV shelter in services and fees.
Would you be open to a pastor, reverend, rabbi or priest helping her? OFten they have advanced degrees in counselling. At least here they do.
I am just throwing out ideas here, the suicide letters and the "I'm ready for a baby" scare me.
IF YOU THINK SHE IS A DANGER TO HERSELF OR OTHERS PLEASE TAKE HER TO THE HOSPITAL FOR AN EVALUATION!!!! Regardless of $$$
Also, and this is hard to say, please please please supervise her with her little brother, it is possible she may molest him as she was molested. It is called a "vicious cycle" for a reason.
There is a book called "The Explosive Child" by Ross Greene. Many have found it very helpful.
If you will PM me your town and state, I will do a search for services, if you like. I will have time over the weekend or next week.
Hugs,
Susie