There are four things I would do:
(1) Change her food. Get her off the Merrick and on to something like IAMS Lamb & Rice, Purina Beyond Simply9, or Royal Canin gastro. One reason I say that is that I spent $$$ and much worry some years back trying to figure out why my dog vomited at least once and sometimes twice every day. I changed foods for other reasons and it was like turning off a tap. Never had the problem again. Make a SLOW transition -- as in, add 1 tablespoon of new food for 3-5 days, then add another for 3-5 days, etc. Add in some Fortiflora too.
(2) Get a muzzle with a stool cup so she can go out in the yard and you can not worry about her eating grass, dirt, etc. You'll both be happier.
(3) Stop spoon feeding her. Establish what seems to be the most acceptable feeding routine for her and stick to it. She's gained more weight than she needs to carry, so she can afford to skip a few meals while you establish a new normal.
(4) If problems continue, get an appointment at Tufts. They are one of THE authorities on food, and they'll help you.
Hugs and best luck.