[Hammy992]

Sounds a bit gross but when I first got my hammy the only way we could find his pee area was by doing a "smell test" on each section of his bedding until we found it. Its quite common for them to pick a corner of their cage and go in that one spot all the time.
If you do manage to find where she's peeing take a bit of the soiled bedding and put it into her potty sand so she can smell it, then put the potty in the area where she's been peeing. Hopefully then it will register that this is her toilet and she will use that instead, which will make cleaning so much easier. If she's using her nest as a bathroom you could do the same thing with the bedding and try to allocate a specific corner for the potty; when she smells whats in it it might convince her that this spot is much better than getting her bed all wet.