Hi... My Cat Has Been Refusing Food For About A

Hi... my cat has been refusing food for about a week, has been vomiting and has diarrhea. She SEEMS hungry and tries to eat, but will turn around and sit down after trying to eat. Just found a swollen lymph node on the left side of where her jaw meets her neck. I have an appointment with a holistic vet tomorrow, but would like to prep myself if you can please shed any light on what this may be. Thanks. My name is Mandy, btw. For the record, my cat (Lady) is about 15 years old. She's a rescue. I cured her of hyperthyroidism and a heart murmur by switching her to a raw diet 3 years ago, plus algae. She's had kitten-like behavior ever since... until a year ago.