Mom takes her oxygen off, walks away from it and then forgets to put it back on, how do you stop this?

I am not sure how I found this site but I'm so thankful to have found it, especially at this time. My mother who has NEVER smoked but has had asthma all her life is now in the final stages of COPD. She has lived with me for over 7 years and off and on before then. Up until a few months ago, she has been totally independent. Now, though, she had a bad bout with breathing in April and the hospice people came into our hospital room and offered to take on her care program. We signed up with them thinking it would be most helpful for both Mother and me! I work 10+ hour days so I was happy for the help on keeping an eye on my mom. They have been helpful to a point but I have now had to ask my siblings to help each day and stay with her because she won't wear her oxygen like she is supposed to wear it. She takes it off and then gets side-tracked and doesn't put it back on until I notice something wrong with her breathing. Now she is also making mistakes with her medicine routine so I feel she cannot be left alone but I'm not sure if I'm hovering too much or I am right about not leaving her alone. Some say I should let her make the decision to wear or not wear the oxygen, but I feel like its my responsibility as her caregiver to ensure her safety and well-being as long as possible. I really really need to hear from others who have or are experiencing this horrible ongoing style of living because I am at a loss and so very troubled. She has a DNR and sometimes she tells me point blank after I have put her back on her oxygen that she is going home sooner or later and I need to just deal with it. I respond to her, "thats fine Mother and I am fine with that when God calls the time, not when you call it". That shuts her down because she is a devout christian, just a tad stubborn.