I agree, with her other changes in behavior, rule out a UTI. And yes, the odor of other cats can trigger this behavior.

Something you may want to consider: you can buy a water proof mattress protector at WalMart, about $30 for the full size bed. It is fitted and goes under the fitted sheet. You can just routinely have that on the bed, to protect the mattress from any and all future issues (cat, human, whatever). Washing the sheets and bedding is a nuisance. But trying to get the odor out of a mattress is very difficult! And if they smell it -- even their own -- they tend to go back to that spot again and again.

I also keep one of those protectors on my sofa, under the slip cover. Same reason, I can wash the slip cover, but getting the odor out of the sofa cushions is really not possible. Of course, I have more pets than you do!