What could be happening with my MIL when she isn't able to eat anything?

Who is giving you information? The patient? Your sister in law? the doctors? Is it possible that there is something much more serious wrong with her and they are not sharing the information? Is she on Hospice?

If you are in charge of her care, I would get her to the ER right away, as Pam says. But I suspect that you are not being told that she has some sort of life limiting condition.

Its through my sisterinlaws shes been going through alot of pains, in her back and stomach, now she cant eat anything, just barely liquids. She was on a feedtube for a little while until she just didnt want it in anylonger and She has the WILL TO LIVE, but just she complains her food has no taste and throws it up. THANK YOU for helping me, the Doctors arent helping much, they are more like she is just old. And she does have the Will to live and trying to get on her feet again, just we dont know what to do for her?

Acid Reflux can create symptoms like that, too. Ask your Mom's doctor to recommend something to settle down the acid, if he/she thinks that could be the issue..

Get her to the ER right now! She has a blockage.

If she throws up everything she ears, she may have a blockage. What tests have her doctors recommended? Is she losing weight ?

Are you witnessing this, or is she reporting it to you? The self-reported of dementia patients can be very unreliable.

Have you taken her to a gastroenterologist? Or to the ER during one of these episodes? Has she had an endoscopy (had a lighted tube put down her throat to see what is going on)?