Sorry I'm late to this. I am SO sorry to read what's going on, and that AMPS is way out of the norm for Ruby so something is definitely going on.
It is unclear to me why the vet was asking you in the first place why she should be admitted? Unless it's for all the reasons
@Tomlin mentions and I'm leaning towards agreeing with that.
I guess it also depends how comfortable and proficient and experienced you are with home nursing as an alternative. I was not. I do not have any history of fostering cats, sick or otherwise, so it was a great weight off me to have her under professional care. The not-eating is now my ongoing biggest fear though, and when Minnie was in/out of the hospital last month it was mostly because she refused to eat...which turned out to be because of the low potassium and ketones. Appetite stimulant and anti-nausea didn't work, even the feeding tube didn't although it helped. - there again Minnie had known and treatable concerns that I couldn't resolve at home (low potassium needing IV fluids) despite the feeding tube. She was in the ICU so extremely $$$.
One thing I learned is that taking the ketone readings with a blood meter (I use the novamax) gives you information much earlier than the strips - strips will show negative for quite a while whereas the blood meter starts indicating the increase. Minnie is susceptible to ketones so I check pretty often with the meter - not that it makes a whole lot of difference to what I do. Feed more, add a bit more water to her food and give the R if BG indicates it's needed. And worry a whole lot. Not necessarily helpful.
Beech Nut baby food is another option - turkey or beef, ingredients turkey & gravy only (possibly chicken). They had it at Walmart.
Hill's AD is my go-to for Minnie now if she's refusing all other foods.
Hang in there. We are rooting for you and Ruby.

