Kathleen,
I'm glad to hear your Mum's surgery will be soon. We are wishing her a swift recovery. My daughter had part of her tongue removed. She also had the mandibulotomy (chin split) and had a modified radical neck dissection. All very similar to what your Mum will have.
Heather did very well after surgery. She wouldn't hesitate to have the other side of her neck dissected if necessary. The surgery was much easier to get through than the radiation. Since your Mum probably isn't having any RAD, she should have a relatively short recovery time.
Wishing your Mum an easy surgery and a speedy recovery.
Rosemary