You aren't going to get a better answer on here than you would from your doctor, so I would definitely look into that second opinion and see what it is. The less invasive a procedure, the better.
A DNC is where they enter the uterus through the vagina and pretty much "cut out" whatever is inside. This can be a dangerous procedure, because the lining of the vagina or uterus can accidentally be punctured, which is probably why the other physician suggested against it.
There is a possibility your mom may need a partial or complete hysterectomy, which is the removal of the ovary, uterus, or both. A lot of times they will do this if there is a concern about cysts being cancerous or causing other major problems in the uterus or ovaries. They're more likely to do this after menopause, and in many cases prescribe hormone therapies to make sure body chemistry continues to function normally.