Full dentures, even in people with a healthy mouth which is free from treatment induced trauma, are problematic for most who have them. The maxillary denture is usually the most stable since it can be held to the roof of the mouth with suction. But the mandibular denture has no way of being really stabilized in position. The muscle attachments in the floor of the mouth and of the tongue frequently work to dislodge it. The movement of the tongue itself does the same. Even the forces of mastication will dislodge both dentures if the occlusion (the chewing surfaces) is not correct and balanced. As patient gets older the bone of the mandible, and the maxilla to a lesser extent, becomes smaller in size from pressure recession caused by the loads of the dentures on it. This also causes the dentures to be less stable. You do not mention if the dentures are new to her, or if she has worn dentures before these treatments. Also whether the dentures are causing her any discomfort as she attempts to eat. If she is new to dentures it can take sometime to get used to them, and what you can and cannot eat using them. New denture wearers in general have a learning curve when it comes to chewing, and getting the bolus of food to the rear of the mouth, since the dentures eliminate the propreoceptive feelings that we all have as the food contacts different portions of the interior of our mouths. We actually know from feel were the food is, denture patients have to relearn this. It is hard for me to imagine someone with delicate, recently healed tissues doing well with any set of dentures. Even those of us with regular dentition have numerous eating issues after treatment. Full dentures are seldom thought of by those who have them as anything other than a very poor substitute for the teeth they used to have. In all my years of dealing in dental prosthetics, I have only come across a handful of people who have said they are satisfied with their full dentures. If you find that the stability of the dentures is one of the problems, the mandibular denture can be stabilized by having two implant placed in the anterior region of the mandible. These can then have a variety of attachments added to them, from snaps to a bar and clip system that will allow the lower denture to remain more fixed in position during function but still removable. If she was not radiated in this area, which many oral cancer patients have not had done, she may be a candidate to have the implants placed. Denture patients with fixed/removable lower dentures have significantly better function that those with conventional implant free dentures.