Hello,
When our animal shelter takes in feral cats that turn out to be FIV positive we still let them back to their usual place, if they are truly feral and otherwise healthy. Nothing would be worse for them than to be contained for the rest of their live, always stressed out and afraid.
However if they turn out to be friendly, like yours and like to be touched etc. we try to find a new home – however still with the option to go outside, if they turn out to be not lucky inside.
Before doing so of course they will be treated against fleas, worms, get their cat flu shots, get neutered etc.
Of course they risk to contract FIV to other cats, but for neutered cats it’s lower, as they don’t get into fights that much and don’t mate.
It’s worse for leukemia. Of the last colony we trapped, most were tested positive for leukemia and they looked like it. They had a (very) bad health status and were put down, as they were completely feral.
I can’t recommend a medication for worms however, as the products will most likely be different from where you live and I’m no vet anyway.
I would keep her on crate rest for 24 hours and see if she improves. This means she only goes out for toilet while on leash, and she stays in her crate otherwise. This will make it easier to determine if it’ll improve on its own or if she needs vet intervention.