Has the vet tested her urine to see if there are any crystals present in the urine, these are often the cause of a blockage, though it is more common in male cats.
Wet food is good as it contains a good amount of water to keep her flushed through.
It could also be an infection causing cystitis where they appear to be squatting all the time, and not peeing where actually there is nothing to come out they just continually feel the need to pee.
I would suggest collecting a urine sample and taking it in to the vets for testing, they should be able to tell you if there are crystals, infection or blood cells present and then take it from there, to be having this recurring suggests there is something being missed, and then they can investigate more throughtly.
Best Regards,
Selena Carnell VN
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