As Cypher says she may not have decided on a pee spot yet. If she's turning the potty over she maybe doesn't want it there - try moving it nearer the house and/or in a corner of the tank. I shouldn't worry - the detolf is so big that wherever she is peeing, if it doesn't smell yet don't worry about it! You'll find out.
She may be peeing in her nest of course or on her hoard. You could check that. If she is then a way round that is to provide a large house and put the litter tray inside it - at the end nearest the door (they like to nest at the end furthest away from the door where it's darkest). Our hamsters have always used the litter tray when it's inside a larger house. They seem to like having an ensuite bathroom
Something like a shoebox is fine - cut the bottom out and a hole at one end of the long side for a door and keep the lid as a lift off roof - that way you can empty the potty without having to take the house out and disturbing the nest and also check in there now and then. Or a guinea pig sized house is sometimes a good size - if it has a flat roof it also doubles up as an extra platform.