Monitor her weight. If she's really not digesting stuff she should start to drop weight. Keep an eye on her urination too, if she can hold water you want to make sure it's not just building up in her body, but it's actually coming out the other end. Keep her really hydrated, diarrhea/ vomiting alone can lead to serious problems if she's not getting enough water.
And yes, I think it's time to seek at least a second opinion. If she's not loosing weight, then you probably don't need to take her to the ER unless she gets dehydrated or starts running a fever or starts feeling really sick.
I would probably switch her to an easy to digest diet as well, start researching that. Things like simple soups with clear broth & steamed veggies are going to be easier on her tummy than meat and cheese. Keep a food diary, what she eats, when, and when she vomits and approx. how much. She may have something simple as a severe food allergy, or it could be something more serious. I would cut out the common food allergies right away, like dairy and wheat, just to be safe. You can start introducing them back into her diet once you're sure that they're not the cause.
But like I said, ER if she starts to loose weight, or can't stop vomiting once her stomach is empty, or if she's retaining water, running a fever or can't keep down water.