Not walking does deteriorate the ability to walk. Sometimes this is a gerrie chair restriction for their own safety, or being bed ridden from an illness, or in a wheel chair because of instability. Once the ability to walk has deteriorated it is difficult to regain it. It is difficult for them to "relearn". The learning pathways of the brain are just not there.
But the other thing to consider is that the ability to walk deteriorated just as the emotional stability deteriorated. Walking, just as emotional stability, ability to feed ones self, and all other forms of cognition are deteriorating simultaneously. Yes, the gerrie chair restriction may have accelerated the inability to walk but the main culprit may have been the disease itself.
If she likes the gerrie chair then why not use it? She may find a sense of security in the nest of the gerrie chair. You can try a wheel chair and see how she does in it if you want. I doubt it will lead to her walking again, and I doubt she will learn how to be mobile in it but there is no harm in trying. You can then make a decision as to which is more comfortable for her and which helps her contentment.
remember there are no right and wrong answers... And if what you try doesn't work you can always go back.