Female cat with recurring cystitis - any advice please?

[Shufflebumnessie]

Our female cat (aged approx. 12.5 - 14 years old) has suffered from recurring cystitis for about the past 18 months. The vet believes it to be stress related and flare ups seem to coincide with being bullied by other cats in the area. We've also recently lost another of our cats which maybe contributing to her current emotional state.
She was a feral when we found her, and as such she likes to mostly spend her time outside (especially at this time of year) so Feliway plug ins don't really work during the summer months.
She's been to the vets several times and is generally given a course of Metacam each visit. We also give her a daily capsule of Feliway Cystease in her food (as recommended by the vet).
She eats primarily wet food and always has fresh water available.
The visits to the vet are getting quite frequent (& expensive!). Is anyone able to suggest anything else we can implement at home that will help reduce her stress levels, and the number of visits to the vet!
Thanks in advance.

Our boy who is 10 also has this (due to bullying by our neighbours cat as well). Unfortunately we are yet to find the magic cure and he’s having a bit of a flare up at the minute. Do you have a ‘safe’ place for her to wee? We have indoor litter trays for him to retreat to which helps, generally you need one tray per cat then one additional one. We exclusively feed our cat Hills urinary stress food, not sure if it works so well but worth a try. Lastly, we have started him on gabapentin which in lower doses can help their anxiety and chronic pain that contributes to the cystitis. He does seem more chilled! Just hoping eventually a combination of these might help my boy!

really feel for you, sometimes feel like I’m at my bloody wits end with the constant visits to the vet. And our neighbour doesn’t give a crap or even try to keep their cat away!

Amitriptyline? It can be used for stress cystitis.