Hi Murray
Michael is quite correct that dementia hits different people in different ways, at different times and on different days [hey that rhymes!]
Whenever there is a change that seems very major, always ask the medical staff whether anything has changed in the caring regime. It may be medications, it may be viruses, it may be other things, including a speeded up progression into the illness.
You don't say which dementia your Mum has. If it is vascular dementia, then the path downwards will be in steps. If it is Alzheimer's then the path down is more gradual.
Typically I have found that some people who have dementia and live in a care home seem to want to rearrange things, so they move furniture and ornaments - even grab other residents and move them around.
So it is not unusual for someone like your Mum to push a wheelchair around. It is a sort of automatic keep fit, perhaps, or just a way to relieve boredom, or a way to feel they are achieving something.
People in homes can become institutionalised and if there are few visitors and too few care staff, then the residents are on their own for parts of each day. These are not dumb people; they want to do things, but what can they do? ....move things about..... After a while it al becomes automatic and I guess their eyes can glaze a bit.
For your first port of call, try and speak to the nurse in charge or to the doctor. Voice your concerns and ask their opinion. Find out what medication has been prescribed, and when it is given.
Best wishes