I was in a similar situation when I split up from my husband. He was not paying money into the joint account for his loans and ran up an over draft. I went to the bank and they told me that they couldn't shut down the account (even after I cleared the overdraft myself) but what they did do was cancel all direct debits on the account and then changed it so that it required 2 signatures for any transactions on the account. This meant that my husband couldn't draw any money from the account or set up any direct debits. Once the account had been left empty for a while it was automatically closed. Tell your friend to go to her bank and discuss the situation with them - they should be sympathetic and helpful.
I had to chase my husband for the money that was run up on the overdraft but I would rather have done that than have the worry of that debt with the bank hanging over me!