Cats are very prone to developing a condition called hepatic lipidosis if they go without food very even a couple of days. This is a very serious condition in which the liver becomes infiltrated with fat cells, disrupting the normal liver function. Once this develops, it will often take very aggressive treatment to get them through this - they may need to be hospitalized for intravenous fluids, antibiotics, other medications and often need to have a feeding tube placed for a couple of months so that they can be given the nutrition they need. This is definitely a condition that you want to avoid at all costs.
Dehydration can also cause major internal organ problems, but cats are very good at conserving water within their body and the instinct to drink water is very strong if an animal becomes dehydrated, that as long as she has access to water, she would probalby continue to drink okay (although you may not see her drinking) until she starts feeling poorly from the liver situation or some other illness.
If your cat does not eat for 24 hours, I would have her checked out by your vet. Also, you may need to start trying to force feed her some in an attempt in trying to prevent the hepatic lipidosis from developing. You can take canned cat food, add water and mix in a blender and force feed this with a syringe. Many cats will really fight this, and that is why this is not generally done long term, but it is so important to keep cats eating .
Here are a couple of websites where you can read about hepatic lipidosis if you would like to learn more about this condition.
I hope this answers your question. If so, please click Accept. If you need more information, please let me know.