Hi Londoner, you don't mention how 'with it' your mother is. Can she speak up for herself? Feed herself and so on?
My mother has had Parkinson's for 12 years or so, and can't do that. She is in a nursing home. My advice would be to keep your mother out of hospital the best you can if she is in the same situation as mine. In my experience, the doctors always want to move you onto 'the next stage' be it a nursing home, a PEG fitted or even death. It's rarely a case of 'Oh, we've solved her problem so she can go back to how she was before'. But again, my mother was never extrovert at the best of times, so can look like she's on her death bed.
As for walking, I used to pull her up the road on a wheelie zimmer, but that all stopped when she went into a home. My advice is to record on a digital camera any footage of her doing stuff that you know she can, so you can present it someone if you need to, otherwise they just won't believe you.
You could try a simple pedal exerciser from eBay for around £20, but otherwise in my area I know of no physio group that encourages the elderly to get back to walking using the same kind of equipment disabled soldiers use, with a kind of hoist and treadmill.
Oh, and in relation to your other query, if your mother is still 'with it' enough to grant you health power of attorney, make sure you get it. Pronto.