Something is not digesting well in her tummy if she is eating grass and gassy.
You said you have her on a new food? What are the first 5 ingredients? It could be one of the proteins that is bothering her? or a grain or carb.
You could also give her a good tablespoon of plain , natural yogurt on her food once a day...it may help with the gas.
As far as the ear mites...I've usually worked on stray cats that had ear mites...and got rid of them by using olive oil. Put a few drops in every day and clean the ears. The oil smothers the mites. It often takes a few weeks of cleaning every day...but you do get rid of them. Some people use mineral oil, or baby oil...but olive oil works good too.
Did your vet not give you medication for the ear mites?
Gina