Michelle,
Please make the appointment for her to see a doctor...then on that day, just pick her up and tell her you are taking her shopping, anywhere...then get her into the doctor's office. I am not kidding. My Dad would NEVER go to a doctor out of fear that came from a bad experience with doctors as a child. He was symptomatic, lost a lot of weight...would not listen to us though we BEGGED him to see a doctor. After ending up in the emergency room and having emergency surgery at 2:30 AM to remove his lower colon, only to be told he has Stage IV colon cancer that has spread to his liver and lungs. He is doing well, so far with chemo....but the long of it is, I wish I had just made the damn appointment for him a long time ago and it would have at least prevented it from getting to the stage it is at.
I realize my words probably scare you and I am so sorry for that. Your mom is lucky to have you because you obviously care so much. Don't be afraid that she will be mad or upset with you for making the appointment and tricking her. Regardless of the outcome (her symptoms could be lots of things, and may not be as serious as cancer), she will likely be grateful and possibly relieved.
Sending you prayers and strength.