Hello Denise,
In case you are now aware, your full name seems to be showing. If you would like to change it there are instructions here.
My full name is showing, how can I stop it. I can see no reason why your niece losing her PIP will mean that she has to move to UC. However, unfortunately, if she has been in receipt of the Severe Disability Premium as part of her ESA she will lose that. (If she gets her PIP back at MR, any missed payments of SDP will be paid back to her.) Her HB and CTR may be slightly reduced, but she should not lose them.
Harsh as it may sound, until her PIP is sorted out she has to find a way to manage without it. The only thing she can do is get the best MR request in that she can muster as soon as possible.
We have guides on submitting a MR which I would strongly recommend that you/she have a look at as part of her MR request.
PIP resources (Scroll down to just below the picture of Liam and Mark)
If you have any questions about the MR process please do come back to us,
Catherine