Broker made me put mother as co- borrower, she wants removed, how should I do this?

In March. 2007, my mother co-signed mortgage, broker told us she could sign off in two years, bank tells me only through assumption, is there another way? She in no way has ever helped with payments, insurance, property taxes, have owned the property since 1994, we were lied to by broker. she was on S.S then and still is NOW, Her name has always been on the deed