What did your vet say?
Chicken broth using the cautions in my last reply, sure, tuna... Weekly to monthly. Very unhealthy. Unless the situation is dire, don't use tuna. Don't leave the broth water out food more than an hour unrefrigerated.
If you've boiled the chicken (NEEDS to be under 100mg sodium per 4oz) in water yourself with no seasonings or any additives whatsoever then sure.
Avoid tuna.
Honestly you'd have an easier time with feeding wet and simply mixing each serving with a spoonful of water.
BTW - Purina is a notoriously bad brand, your vet isn't a feline nutritionist so don't exactly model your opinion off of what they say alone - science diet and Royal canin both are lackluster and contain biologically inappropriate and unhealthy ingredients.
I would also suggest looking into...
Food rotations are when you have several brands and types of food, primarily different proteins you alternate through daily, for example,
A sunday
B monday
A tuesday
B wednesday
This can be 2 to an infinite number, every other day, every week, etc. Aids in preventing food intolerances and...
Anyways make sure to research those plants they list in the link above as most are extremely toxic and I'm sure you're not interested in killing the stray but rather deterring it. And don't fall into the thinking trap that cats won't eat a poison plant. :)
Could you get a blender, and blend it to smoothie consistency? You could slow boil chicken or any meat of your choice without seasoning or salt into a thick broth to add to it
Repellent around the window means your own cat will no longer be able to enjoy it.
What I'd suggest is a motion activated sprinkler of sorts, jackson galaxy sells air canisters that are motion activated as well, but I'd wager that it'll take more than air to ward off ferals.
You can use diatomaceous earth in the garden, I don't condone dangerous chemicals and poisons AKA what kills fleas; included indiscriminately in those flea treatments and toxic collars, I'd inforce regular sanitization of your home with full vacuuming, wiping things down, taking every single...
Not to be offensive but cat's genuinely are not intelligent enough to force themselves to throw up to get some kind of response from you. That's a bratty human thing.
You got it !! I only ever get to hear her nasally whining when she's begging !! Thank you very much, and holy moly Sansa is a goddess!! They could totally be twins, I always wonder if specter is gonna fill out like that and look like an adult but she's bordering 3yrs in human time...But she...