How old is she, does she get to go out? They can be stressed by very small things, one of mine suffered awful bladder probs from around the age of 8 months to 3 years, he didnt tray hop but passed good sized wees full of blood
like your cat he had nothing 'wrong' with him.
I used cystaid daily (starting on 2 capsules) and feliway (not sure if it helped!) and tried to keep him in mind before doing anything remotely scary. I changed all the trays bar one to a fine clay litter that was nicer for him to use.
Hes now 4 and about a year ago he suddenly stopped weeing blood, touch wood hes ok.
One of the most useful things for him was metacam, you would need to speak to your vet about it but sometimes a day or two is all they need to break the cycle (til the next time)