Cats can't tolerate spicy food and it can cause gastrointestinal upset, like diarrhea and vomiting, plus irritation and burning in the mouth.
For the moment, you can try giving her a small amount (1 oz.) of fat-free milk (Lactose-free, if you have it) and this might help stop the burning in her mouth and stomach, if she is experiencing these symptoms.
You had said she was drinking a lot of water, so, that's good.
Here is information re: Pepcid AC regular strength--10mg. Give 1/4 tablet every 12 hours. Generic is Famotidine.
If you have a regular rectal or digital thermometer, try to take her temperature to see what it is. Just lubricate the thermometer with plain Vaseline or plain KY Jelly and insert into the anus about 1/2 and inch, then remove and read. Normal temps for cats are 100.5 -102.5; if she has any higher than that, she has a fever. This could be from the spicy food or something else may be going on, so that's why it's important to have her seen by a vet, as soon as possible.
Because of the possible ingestion of garlic and onions, watch for any paleness of her tongue, gums, paw pads, ear tips.
Info on Care Credit:
I hope all will be well with Tigger and look forward to your update!