need opionion on what's next for my 9 year old cat found as stray 4 years ago

Hi - I'm new to the group and new to be a cat owner.  My elderly father had a stray cat find her way into his house 4 years ago.  She was an indoor/outdoor cat and he really didn't do much for her - just feed her and give her a place to stay when it was hot outside.   She started not eating much and spitting up a foamy stick liquid if she did eat.  I decided to take her in and she continued to spit up this liquid.  She also came to me with a fever of 103.  I took her to my vet who gave an injection of antibiotic and diarrhea as well as pills to try for the vomiting.  This didn't work so I took her to another vet that I had previously taken my dog to who said it might be IBS and gave her an injection of steroids and fluids for dehydration. He kept her for the day and feed her which she proceeded to throw up in their office.  I picked her up in the afternoon from his office and fed her at dinner time her usual food.  She kept it down but still spit up a watery portion with food mixed in.  I don't know what is causing this. The vet ran a complete blood screening and found everything in normal range with some dehydration which was coming from the vomiting.  Does anyone have any advise of what it can be from?  She wants to eat and drink but right after it, she leans forward and vomits a gooey substance with light traces of digested food. 

Vomiting is not normal in cats and cat be a sign of IBD. My cat had a chronic vomiting problem and i was able to treat him by shaving him, switching him to an all wet diet and giving him supplements from vitality science. Here is a good video on vomiting in cats 



and one on IBD