When do I know it’s the right time to withdraw the feeding tube from my mom?

My mother is 53, and has been suffering with a rare form of MS for almost 15 years. In 2009 after suffering several strokes and being in a coma I made the decision to let the doctors place a PEG tube in my moms stomach. At the time I felt it was the right decision, however now I am questioning it. I am an only child and my mom and I never discussed artificial feeding before, but I didn't want to lose her. Today the doctors have changed her diagnoses from MS to "Failure to Thrive". She is alert, and talks to me, even though sometimes it makes no sense, but when she has one of her good days she tells me she wants to die, and she can't take being in a nursing home anymore. I know the nursing home is my fault as well, but I was not able to give her the specialized care that she neded and after fall after fall when I was not home, I had no choice. The doctors have told me that the only thing keeping her alive is the feeding tube. Other things have already started to shut down. I feel so conflicted because I want to do what is best for her, but at the same time I feel like I would be the one killing her. She is all I have and I know even saying that I want her here when she is telling me she is ready to go is selfish, but I don't know what to do. Do I listen to her request and stop the artifical feeding or do I let them keep feeding her and when it's her time, it's her time...