Maybe she’s one of those “bite first and decide if it’s food later” personalities, I’ve met a couple rat snakes and a juvenile woma like that (where anything that’s warm and moves is food until proven otherwise) but never a ball. That’s very odd for a ball python. You should check out “Snake Discovery” on YouTube, I believe they have a Rosy boa like that and they may have some ideas you can try. I think they put their email in the descriptions of their videos.
It’s a good thing you’re making an appointment with the vet. RI can definitely impede a snakes ability to smell, but I would think the feeding response would be hampered by the illness as well. Snakes usually don’t tend to eat well when they’re sick, and I wouldn’t expect her to be as food aggressive as she is if she’s also ill with an RI... so strange. As for stool samples I would assume the fresher the better but asking the vet office will give you the best answer. Please keep us updated