Possibly an ultrasound scan of her bladder
, and certainly urinalysis to check for bacteria in
the urine. If it is a bladder
infection, it's possible a course of antibiotics will clear it.
If it is Pyometra, then it is serious and she needs her womb removed.
If it is a bladder issue then that is also serious too, and needs attention quickly.
Surely the vet would discuss this with you? Or do some more investigation?