Poor Zoe, anything bladder related is so uncomfortable.
The vet will probably want a urine sample first. If possible, collect some before you take her.
Out of the tub would be the best option. If you still hours away from taking Zoe, refrigerate the urine.
Lots of times, when the kitty arrives at the vet, the bladder is empty, and the vet can only guess if it is a bacterial infection, or feline lower urinary tract syndrome, which is just as uncomfortable, but doesn't involve bacteria.
Good luck and best wishes to you and Zoe!