Although it sounds like the car is not worth much, she might try to sell it and then come up with the difference if she wants to save her credit. If she is in good standings with a small local bank or credit union they may give her the difference and she will need to pay it back. But most of the bigger name banks, Chase, Bank of America, etc usually won't negotiate. If it gets re-poed it will be on her credit for 7 years and she will still have to pay the diffence from what the bank sells it for. If the bank sells it for 3000 and she owes 7000, they will come after her and her daughter for the difference.
There is a financial guy who is on the radio on 1220 am at 1pm and goes until 4pm. Dave Ramsey is his name and it sounds like your friend really needs to tune in. He talks a lot about this kind of stuff. People are always calling in for advice and he is a straight shooter. She also sounds like she needs to get the book Boundries, to handle what her daughter has done to her. And it will also help her not do this kind of thing again.
I feel for your friend. After my dad died, my brother came to me and asked me to co-sign. He had all of the family give me a guilt trip about how my dad would have wanted me to help him with a second chance. He defaulted on the loan 6 months before it was due to be paid off and it was re-poed. Not only is it upsetting to ones credit, but that someone they love would betray them and seem to not even care is VERY hurtful.
Hope this helps.