Well the standard reply is to get that cat to a vet.  Cats are very good at
hiding their illnesses, so if they aren't eating, then there is a serious
problem.

But in the mean time, offer ANYTHING you think will tempt your cat to eat.
Chicken, meat, tuna, or any human food she's shown interest in the past.
Meat baby food is always a huge hit in my house.  When my little one was
dying of FIP, meat baby food was all I could get him to eat.

Good luck!

First & foremost, has she been to the vet?  If not, that's absolutely
necessary - immediately.  Like tomorrow - or even tonight.  Explain that she
isn't eating at all, that she's weak & emaciated, & they'll squeeze her in
for an appt.  That's good that she's drinking, but she really needs to eat
if she's going to beat whatever's ailing her (could be any one of a bunch of
different things).

Secondly: you can try baby food meats (no onion in ingredients, though) & a
canned food - Hill's Prescription Diet a/d, available through the vet is a
food she may take to.  It's also a very fine consistency & is good for force
(syringe)-feeding when necessary.

Thirdly: ask the vet about an appetite stimulant.  For example,
cyproheptadine/Periactin acts as an appetite stimulant for cats - although
it's an antihistamine for humans.

Cathy