I work in a clinic and the honest answer is that we would want to hear about it, but over the phone rather than as an emergency walk-in, based on what you have described. Most practices will triage this on a call for free and it takes five minutes.
The things that move it from "call in the morning" to "go now" in our triage are: repeated unproductive retching with nothing coming up, a hard or painful belly, hiding and refusing to move, pale or tacky gums, no urine in the litter tray, or any chance she got at string, tinsel, hair ties or a plant. A cat that is eating, keeping it down and playing an hour later is a much more reassuring picture than one that is quiet in a corner.
I would hold food for a couple of hours rather than offering more, keep water available, and write down every episode with the time. That log is genuinely useful if you do end up going in.