Brain met vs. lack of oxygen - 1263385

My mother has Stage 4 NSCLC. She has had it for quite some time and has been through a lot with this disease. Recently my mom has had growth in a tumor in her neck. It has occluded the left jugular vein. The other arteries and veins are open, but they are compromised by the tumor. Her left diaphragm is paralyzed from the tumor, so recently she is having a very difficult time breathing (and the tumor in her right lung is also growing) and is constantly on oxygen. She previously had a brain met, but as of her last MRI (about a year/year and a half) all was well. Last week I started to notice that she was having trouble finding words for things. She also seemed to not know names, etc. And was complaining of a headache. We mentioned it to her doctor, but he didn't make much of it (I think we are to the point of hospice). Anyway, starting on Saturday, she began hallucinating. She thought someone was in the house, got herself dressed (which is very difficult for her) and said she was going to my sister's house etc. I'm wondering if there is any possibility it is something else (rather than another brain met) we should look into. For instance, maybe she is not getting enough oxygen - she is on 3 liters, perhaps she needs more,etc. Or would hallucinations like these be more likely to be a brain met? Thank you so much for your help and all you do.