Sounds silly but it could be as simple as her way of making sure she doesn't fall again? We all know that the shock of falling over gets worse as we get older so to fall several times in the place where you should feel most secure must shatter the confidence, especially if it leads to a stay in the local NHS establishment.
A similar thing happened with my Mum - she had a series of falls in her own home and ended up in hospital. Fortunately she was not hurt, but she was odd for several days after and has since refused to leave her armchair unless there is someone to help.
If I look back on that time (Feb), she did go through immense trauma. She fell one evening in her own home and in the presence of TWO carers (despite the lunch carer noting Mum was particularly wobbly that day). She was then strapped to an immobility board and had to stay like it ALL NIGHT until the X-ray dept. opened the next day. She was really weird in herself for several days after this, some of which was due to dehydration but some of it was sheer SHOCK. What a terrible experience for anyone to cope with, never mind an elderly lady with dementia.
When she came home she refused to leave her armchair unless there was an extremely good reason for doing so (initially,just to go to the bathroom). Nine months on, she still spends most of her life in the armchair but in herself, she is SO much better. It's almost as if a burden of fear and expectation has gone from her shoulders. I feel that in some ways, she is more contented than she has been in years and this has allowed her to "be" as well as she can be (eating better, sleeping better etc.).
Initially there were all the fears about pressure sores, thrombosis etc, but in actual fact, she has got better since we all accepted the armchair situation, not worse. The DNs visit regularly and the pressure sores that she HAD have healed; she's happy enough to be taken to a Day Centre twice a week, and whenever she has anyone come to the house, they take her for a lap or two of the sitting room (with frame of course).
I'm not saying any of this will help your dear Mum Forman, but I know how strong willed my Mum was in health and even though she has lost a lot of control in her life, my goodness, the strong will lives on. xxx