Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry for this concern about Jasmin.
It's possible that this behavior is secondary to late onset Inflammatory Bowel Disease or systemic disease (issues with her kidneys or thyroid, for example, even though she's not showing other signs), or nausea for whatever reason.
But, regardless, I do have a few suggestions which may be of help:
1. Consider a change in diet although I realize that you indicated that you did try a different food. But, if it wasn't hypoallergenic and/or one with a novel (new) protein, then this may be why she continued to vomit especially if she's developed IBD. I also suggested canned versus dry (if the patient will eat it).
Feeding grain free may help in some cases but others to consider would be Z/D (from your vet), or Natural Ba***** *****mited Ingredient Diets, Nature's Variety Instincts line, Evo duck or venison, Nature's Variety Frozen Raw Medallions (I recommend that they be zapped in the microwave for 10-15 seconds on each side).
2. Consider giving her 1/4th of a 10 mg tablet of Pepcid AC (Famotidine) once or twice a day. This is the same human drug which you or I would take and is available at just about any pharmacy.
3. Add a feline-specific probiotic to her food every day. Forti Flora is a really good one which is a powder sprinkled on the food. It's available at many local pet/grain stores or can be ordered online.
4. Consider blood work if it hasn't been done since she's started this behaviror.
I hope this helps. Deb