It sounds like she may have hyperthyroidism, which is very common in older cats. Vomiting and weightloss are the most common signs. She really does need to see a vet right away. If she's not keeping any food down, she's at risk for hepatitic (sp?) lipidosis, which is a liver disease that can be fatal. Even if she is getting some nourishment, if she is hyperthyroid, it can cause long term health problems, include heart disease. As much as she hates the vet, she really needs to go. I would wrap her in a towel and put her in a carrier (or a box, if necessary). Since most carriers have open areas on the sides, you can cover it with a blanket to help keep her calm.
Also, if you go with your mom, one of you could go in and let the vet know you're there while the other one waits with the kitty in the car. That will minimize the time in the waiting room with other animals. Good luck!