I'm not a rabbit expert but you could bring her litter box with you when you go to the vet for the urine check.If she still doesn't pee in the litter box at the vet then you may have to find a way to do it at yours but I don't think it will affect you bunny much unless you were trying to test...
I would advise not to separate them if as I have heard the rabbits can forget each other in the matter of hours.Only do so if the fighting is extremely aggressive and not just chasing around or play fighting.I have 2 males(around 8 months old) which are brothers and occasionally the other might...