It sounds as if she is very stressed and havent you just got a new cat............Pandora?
By her sitting outside by herself in the rain it sounds like she is trying to get away from something............meds, you, other cats??
I have only a little knowledge og cystitus and it was stress induced and Misa had it,,,,,,,,,,,,,it was when Franta was ill ands was getting lots of attention. Misa is very jealous and this brought it on.......nothing has changed and he is still very jealous and can get very upset.
Misa has just started trying to sleep on the bed and tries to flump on top of the birmans to get them off,,,,,,,,,,,,,,,,,,,so wondering about Fifi with Pandora ??
I do hope she gets well soon