I had another good idea. The infection my cat has is from bad gut bacteria and apparently weak to a good bacteria called Lacticaseibacillus rhamnosus, so I walked to go get her some plain Greek yogurt specifically containing that. My knees are screaming and I couldn't find a small tub, only a big expensive one, but got hold of a lactose free kind and she's just eaten a spoonful. The antibiotics might nuke everything so I might give her a little yogurt each day of her antibiotics and then hit things with the bought probiotics once she finishes.
Melbcat likes it a lot so if her stomach handles it she might have a snack each day or a dollop with each meal for the long term. It costs and I don't know if I'll be able to eat it as well, but I could freeze it in cubes (if the bacteria will survive well) and it will be cheaper than spending hundreds every time she gets sick. Fingers crossed it helps. I'm really trying to avoid further antibiotic resistance π¬