Oh geeze, I can't imagine how upsetting that must have been to find. I haven't tried it on cat vomit specifically but I know seltzer works really well on a lot of biological stains
Oh man!!! That's a stumper! Congrats on having a truly novel problem! I guess dab at it with a damp cloth, quilt and then wash? I think that's what I'd do.
I don’t have advice, but that cat looks very satisfied with itself. Did you not pet it the exact number of times required that day?
Yep. That happens. Beautiful quilt and you're lucky that you should be able to replace that area if it doesn't wash out.
Well, the good news is that it’s just on the white fabric. Since it’s not quilted there yet, I would remove any basting/pins from that section, put a thick towel between the top & batting, & spot treat. Start with wiping if off with a damp cloth, then dab with stain remover (I use an OxiClean-based spray on my carpets for cat barf & it works great, even for the dark orange prescription food that stains like crazy). You can try hydrogen peroxide and baking soda instead of a commercial spray (just like you would for a small bloodstain). The longer you wait to clean it, the worse the stain will be, so I wouldn’t put it off. Good luck!
I use Folex for my cat’s vomit, and it works well! I’ve only tried it on carpet before though, not on a quilt.
Seeing as it’s not quilted in those areas, I would try to rinse it off by hand and if it doesn’t work cut that part out of the top and add clean fabric.