Hi there! Sorry this happened, ketones can be scary!
I have a couple questions that might help direct advice:
Are you home testing blood sugar?
How much vetsulin and how often are you giving it?
Would you be willing to test ketones at home (urine dipstick)?
Did the vet draw a potassium level?
What are the fluids they gave you (it should say on the bag)?
For a start, with ketones, it's important to have 24hour insulin coverage. This is called a "basal" or background insulin. Vetsulin has about the same duration as other zinc insulins, so maybe 8 hours or less in cats. In order to maintain a basal rate and eliminate ketones, 3 times a day dosing is better. Even better than that would be to switch to a long acting insulin such as lantus or levemir. Cats prone to ketones should always be on a long acting, in my opinion. Ask your vet if you can switch.
Also, dehydration gets really serious with ketones. The subQ fluids are good. Oral fluids are better as it disrupts electrolytes less, but sometimes not possible. Plain pedialyte is good for oral replacement as it has electrolytes, you can mix it with the food your are syringing. A normal cat needs about 300ml oral fluid a day, more when ketones are in play. This includes the moisture in canned food which is probably 120-150ml/5.5oz can.
Food is necessary. Feed her anything she will eat. Even treats, even dry food. Whatever. You can adjust the insulin to compensate. Eating+appropriate insulin is the only way to make her body stop burning fat and making ketones.
Ask your vet about a anti-nausea (not an appetite stimulant). That can help your cat eat earlier and make her recovery faster.
Low potassium is a major and common complication of ketones. It's VERY important that this is tested, and supplemented if low. Low potassium can lead to fatal heart arrythmias, and muscle weakness that can slow recovery.