I recommed having her seen right away. The change in nose color is a sign of anemia which can be very dangerous. If you can look at her gums, if they appear pale or white, this is another danger sign. Given her symptoms which are very general, I cannot tell you what is wrong with her, but something is definitely wrong. Cats don't stop eating for no reason, and lack of appetite, lethargy and hiding are all signs of illness or pain. She could be injured or the mouse may have been poisoned. Most conditions are easier treated the earlier they are caught so I would not want you to wait on this, and if you can get her to eat something in the meantime that would help. Lack of food can cause liver problems which can compound the problem and become a serious issue in itself.
Please let me know how she does, I'll be thinking of you!
Anemia in a cat is not low iron count. Pale gums and change in nose color can be indicators of it. It is also not a condition that happens on it's own, rather a result of something else. Causes can range from parasites to kidney failure, and these are not things that you can guess at and treat for at home. If it has been days since she ate, she could have a liver condition called fatty liver. This requires force feeding until it clears, and could take days or weeks to recover from. The strange chewing you are seeing can be a symptom of that.
While it is great that you are getting her to eat, if it is not her normal amount, she could still be in danger.
I realize vets can be expensive, but treating for anemia is not as simple as that...you need to know what is causing it. For more info on anemia, click on the word anemia in my first post. It is a live link to further info. Here is another.
I am sorry that I cannot recommend a home treatment, given her condition I think she should be seen. With most conditions, the sooner treatment is sought, the less complicated (and less expensive) treatment can be.
For financial assistance try http://www.carecredit.com/ which is a credit card that allows you to finance vet bills over time with little or no finance charges.
I hope she will be just fine. Please let me know how she does!