Hello,
As with any fear associated behavior it is best to start slow and gentle and begin to gradually reassure them that things are ok. In some cases I use treats, a short lead or even a dog bed to place a good reward with conditioning out a fearful reaction. Things like placing her in a crate she is comfortable in to relax her near the threshold and then walking slowly outside and giving her treats as you go or as she approaches you. Often you will find there is a specific point that they won’t advance past. This is the time to sit, be calm and gentle and reassure her that things are ok. Never do anything too fast, and don’t force her. You have to be calm and gentle so she learns trust. Don’t yell and never hit even if you are frustrated. I also think that electronic fences are not ideal for the reasons you have learned. Try leash walking and building trust and then start conditioning her out of her fears. Try also looking at Victoria Stilwells stuff. She’s great! Google search her name for lots more training info.
What has your vet done so far for diagnostics?
Just blood tests, and they always come up normal.
I would worry that something else is wrong. Could this be allergies? Could she be getting into something outside? Have you considered keeping her inside due to her age? You *may* be able to better contain her vomiting if you can control the environment more closely.
I hadn’t thought about allergies, are there any common outdoor cat allergies I should watch out for? When she’s outside she’s always on a leash so I can kind of control her, but every once in awhile she’ll get her mouth on some grass. I don’t use pesticides and none of my neighbors within a half mile of my house use lawn pesticides. The cyclical nature of the vomiting is what confuses me. She’s at her worst May and July, but ok June and August. You’d think she would be exposed to the same things all 4 months.