I am not qualified in any way, and you must take the advice of your vet, but I nursed both Dushka and Persil through life threatening illness when they were very small. I would never let a 7 week old kitten go more than three hours without eating and drinking, and in fact usually fed them a little every hour except overnight when I would let it go a bit longer. I fed both of them by syringe for quite a while - Dushka for three weeks, Persil for nearly 4. Even after they started to eat by themselves I continued to supplement by syringe for a while to build up strength and keep hydration. Above all get liquid into her - I used to try and make sure it was nutritious too - homemade saltless chicken broth, goats milk with some egg yolk beaten into it, and you can make the kitten glop whose recipe you can find on this thread. It is very easy to feed by syringe when they are small - they quickly cooperate. Hold them by the scruff against your elbow, put the syringe into the side of the mouth and press gently, making sure they get a little at a time and don't choke. Around 20ccs an hour is enough at that age, increasing by 10ccs per week.