Bless your mom's heart. A laproscopic procedure would be pretty risky with a mass of that size, personally to me. I had a mass of 28cm and I had a normal incision surgery, and I would not of done it any other way. Please make sure your mom is seeing and having surgery done by a gyn/oncologist. Best Wishes to you and your mom.
Just remind her it is important to keep an open mind and to listen to the doctors. Is she seeing an oncologist? What test have they done so far? They will need to do some blood work and maybe a CT and/or ultra sound. For her over all health I would just suggest to get it out sooner than later. I have one cyst that is 22 cm and surgery is next week. Can not wait to be done but also waiting for results is very scary. With a cyst that size the will most likely want to do a larger incision. Mine will be from the pubic area and can go above my belly button. I hope the best for both you and your mother. Please keep us updated on her progress. Take care