Any tips for getting an elderly women to use oxygen?

I really don't know how you would get her to wear it if she doesn't want it. My MIL was on oxygen when she was in hospice. She would  take it off. Her daughter would put it back on. She got aggravated with her daughter and said " if I die, I die". I wonder if your GM will use it on her own when she really needs it? I've known others not to use it when prescribed for night time usage. My late BIL (COPD) did not want to be bothered. He developed pneumonia and after a month in the hospital he passed at 77. Of course the entire time he was in the hospital he was on oxygen and more. 

I said, "Dad use your oxygen, we paid extra for it."
That made a BIG difference for my dad.

Have they put on a humidifier to help keep her nose from drying out? That made a BIG difference for my mom.

Why don't you call the DME provider and ask if there are other options? I have only seen the nasal cannula that is tubing with "prongs" that fit into the nostrils, but there may be other options.