The doctor gave my mother some exercises because she has trouble with walking and balance, but they aren't working. What should we do?

It could be medications, an undetected stroke, or onset of an illness such as Parkinson's. Also, inner ear infections through off your balance and take awhile to treat. Does she feel lightheaded? Does she have high blook pressure? Vision problems (effcts balance too.)?
Mobility is key to a senior staying as independent as possible. Have been working on this with my Mom. She just finished 2 weeks in rehab and it has helped her tremendously.
Have you considered in-home physical therapy? It is so important for seniors to keep moving and maintain their balance.
Mom had arthritis that set in near an old injury. Massage really helped.
Good luck...let us know what you find out.
Lilli

Has your mother had any falls yet? It sounds like you are concerned about your mother's risk of falling for good reason, because of the tone of your post. A second opinion certainly could only help, What is the "medicine" that she won't take? When you say you see her "struggling", how specifically do you see her struggle? Sometimes , unfortunately, it takes an actual fall to convince an elder that he/she needs assistance of some kind----to see a doctor, get a cane or walker, get help in the home, etc.