Leila, our six-month old cat, is being attacked by a neighbourhood cat, Jasmine. I know it's a territorial thing, but Leila stays in and around our home and, in theory, it's her turf. Jasmine is much older and I've seen her around prior to our adopting Leila. I don't know Jasmine's owners but even if I did, I can't ask them to keep Jasmine indoors.
Leila loves to go out and would be quite miserable if I kept her confined. Any suggestions?
I'd make her feel unwanted if she's in your garden, then. A thin jet of water from - say - a garden plant sprayer won't harm her (of course) but would certainly discommode her. (Cats usually hate being wet.) She ought to get the message.
Have you a microchip flap for your own cat if she uses a flap? It would be unfortunate if Jasmine was able to come into your house and invade Leila's safe place.