All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
You are obliged to return the money to your friend in one lump-sum unless she agrees that you repay it on instalments or that you face financial difficulties and you are unable to return it (in one lump-sum), in which case she should give respite to you until you become able to repay.
As regards your friend not willing to discuss the matter of loan with you, then this does not make you acquitted from the liability of repaying it. However, if you repay the loan to her any way she can get it, then, in this case, you are acquitted from liability.
Allaah Knows best.