Mortgage loans are generally non-assumable however a lender may make an exception when someone has passed away. When an exception is made, it is on their terms and "they" will decide the criteria.
Read the terms and conditions of the present modification. Although they enabled your mother to remain in the home, they may not be favorable when compared to today's market place. It could be that you may be able to qualify for a new mortgage at a lower payment, in which case the existing loan would be paid in full - and you would begin again anew.
In the meantime (while you're doing some research) keep the payments current.
Should it happen you don't understand the language contained in the modification, consult with an attorney - and you may need a probate attorney to settle her estate despite your name appearing on the deed.
I'm sorry to hear of your loss and wish you the best of luck!