Friend, I am sorry Wuss is not feeling well. In response to your question, vomiting and diarrhea can be caused by disorders affecting the gastrointestinal tract or secondary to a systemic disease. So, every time we see a cat vomiting and having diarrhea we need to figure out if this a gastrointestinal problem or something else going on in the body to establish a treatment plan. This can be caused by many different medical conditions. It will be difficult for me to determine the exact underlying cause without a hands-on examination and some testing. But, common causes are dietary indiscretion, ingestion of a foreign body, infections, kidney or liver disease, hormonal disorders, etc. to name a few causes. To determine the exact underlying cause Wuss would need a hands-on examination with your family veterinarian and some testing (blood work and x-rays) as an initial screening test. Treatment will be based on exam and test results. In the meantime, in any case of vomiting or diarrhea the first thing to do is give the gastrointestinal tract time to rest. This is what you can do:
1- Do not give things like Pepto Bismol or Imodium. Start her on Pepcid AC (famotidine) 10mg 1/4 tablet every 12 hours for the next 2-3 days. You can buy Pepcid AC over the counter in any pharmacy.
2- No food or water for 4-6 hours. Need to give her gastrointestinal tract time to rest.
3- After 4-6 hours offer a small amount of water. Wait half hour, if no vomiting, offer a small amount of rice (50%) and boiled boneless chicken or ground beef (50%) 4-6 times a day. Keep on this diet for several days then wean into regular diet.
4- Follow up with your family veterinarian for a hands on examination as described above. If cost is a concerned I would look into your local ASPCA or Shelter where they often offer veterinary services at a lower cost.
My goal is to provide you with excellent service - I hope I've provided the information you were seeking, if you feel you have received anything less, please reply back as I am happy to address follow-up questions. Kindly rate me when you are done.