If appointment letter is not signed it is not difficult to resigned from that company because technically yours friend is not an employee of that company**, but as per information provided by you company is not look alike professional one so if yours friend resigned that company probably refuse to give reliving letter and Rs. 10000.
It is my suggestion talk to reporting boss and convince him that he help her to get a respected full separation.
Note- I am assuming that she did not signed PF or ESIC document **
If it is DD, then the money is lost.
If it is a cheque, you can give stop payment order.
The bond is meaningless in a situation where employer failed to pay salary regularly and on time. There is no reason to even look at the validity of the bond