In reading my previous post this AM, I realize that it came across a little harsh as to priorities. I'm sorry, this has been a week of several OCF acquaintances losing their battle, and I'm a little sensitive to priorities right now. It has nothing to do with whether or not your esthetic concerns are important, they of course are. The whole person is being treated, and esthetics and self-confidence are of course a genuine and valid concern.
If your sister handles the radiation treatments well, there is an intermediate step that the prosthodontist may take to give her more comfort in public or at work. This is commonly referred to as an "immediate denture," which while still made of hard plastic and plastic or porcelain teeth, is lined with a soft resilient liner. The soft liner is readapted to the changing contours of a patients mouth every couple of weeks in a simple chairside procedure. Since this denture is for esthetics primarily more than chewing, it is likely that just the maxillary denture would be initially made, as this impacts the shape of the face and the smile more than anything else. But even this step may be some time off. The doctors are going to want the soft tissues to heal from the radiation induced mucositis as much as possible first, and that means after radiation has ended.
One of the issues that she should be aware of, and working on during treatments, is radiation induced trismus which you can read about in the web site. With totally edentulous patients, the tendency for the vertical dimension between the two arches to decrease is more likely since there are no teeth to help maintain the space. As the effects of trismus become more pronounced, this will potentially cause problems later when her final dentures are made. It is important that she maintains this inter-arch space through stretching exercises throughout her treatments and for months after radiation has ended.