[Ellie May]

Is this vomiting (with heaving) or spitting it up?

Undigested food after that amount of time could mean there is some sort of blockage slowing things down. Has your vet looked in to what may be going on with her esophagus and/or stomach? I would wonder about things liek megaesophagus. Sometimes metoclopramide is used in cases like this to get things moving along, but of course that is only under a vet's supervision.

I'd go ahead and get a second opinion if the current vet isn't looking into it.