s age is ( unfortunately ) often a sign
of uterine cancer. They may be performing the
MRI scan to see if there is any spread
of cancer outside of the uterus, for example, to the lymph nodes in the pelvis. Sometimes the extent of the disease can determine what type of therapy is best--for example--radiation therapy instead of surgery.
I don't mean to worry you unnecessarily, but I do think you should prepare yourself and your mom for this possibility.
Hope this helps!