I am sorry she is not feeling well.
Cats that eat dry can have bouts of dehyration.Indigestion is caused by inadequate chewing. Vomiting is very common. When acid reflux builds up in the stomach, they begin to vomit. Even if they have always eaten this,, they often become intolerant to corn and gluten which are used as filers in most supermarket cat foods.Vets push science diet because they sell it but it is not a great food as it too contains corn and gluten.
Lack of fluid in the bowel also leads to vomiting, Ingested hair can also be a factor.Anorexia for any extended time leads to liver damage and causes nausea and vomiting as well.
I would add some canned or baby food for her
Serve the two foods separately - do not mix them - add a half pepsid a/c tablet, crushed up into the wet food one time a day.
Put hairball remedy or even plain vaseline on her paw for her to lick off as well.
If her tummy needs a rest, feed baby food with no onion or garlic for a few days.
If she wont eat, and your cat is not diabetic begin by giving her two droppers (cc size) of unflavored pedialyte every ten minutes for an hour. Next water down(plain water) canned cat food or baby food chicken or turkey with no onion or garlic and give only one dropper every ten minutes for another hour. Wait two hours and repeat both. When she feels hydrated she will lick up the gruel on her own.
Give her droppers of unflavored pedialyte a few times a day to make sure she stays hydrated.
If she throws it up have her seen immedately.
Please let me know how she is doing. I will always be here for you.
I hope she feels better very soon.
Sincerest best wishes,