You and your vet have covered your bases. Nothing you can do will make her immortal.

No need to continue to indulge in stressful tests. Follow your best instinct and give her nurturing care to maximize her comfort in her decline.
Consider if there's a level of small frequent meals that don't trigger her vomitting. Conversely, several hours of water only fasting might be healing. Try variants on your water. Distilled? Spring? A little ACV or baking soda added? These have all been known to add comfort to some. Mixing warm water in her food ("mouse-body warm"

) might settle it better. I've had luck with that in several situations.
The milk thistle sounds promising.

I hope you hear from the vet on it. It sounds safe to me.
Let her guide you

. Cats tend to be more sensible about end of life and palliative care than we are.


