Hi OP
Really sorry to hear about your mum.
to you both.
With my professional (physio) hat on, I would say that she should really have a proper assessment with one rather than you buying one for her. This would also mean she’s been taught how to use it correctly (sounds daft but is surprisingly necessary) However in the real world, this might takes weeks so in some respects I wouldn’t blame you for going ahead and buying her one.
A few points to consider:
You’ve mentioned she’s very overweight, you’ll need to check the weight limit on any frame you get. She may need a bariatric frame.
If she’s pretty good on her feet and doesn’t need to put loads of weight through the frame, she’ll probably be ok with a wheeled frame. A non wheeled frame will be sturdier but much slower for her. In my experience people tend to get frustrated by frames without wheels if they can move at a reasonable pace (ie not one step, rest, one step, rest) And don’t use them
The height of the frame needs to be correct. The handle should come up to the line of her wrist.
Does she have any steps in the house? If so you might want to consider having one at the top and bottom of the steps
In terms of using the frame, she should never pull up on the frame to stand up from a chair and she must always let go of the frame before she sits down.
I’m sure there are other things but I’m feeding my baby at the moment so I’ll have a think and come back to you