I'm sorry your Family is going through this. This disease is so hard on patients and Families. I do agree with Christine's advice re Hospice. Phone them today and get all the help and advice you can.
Your post mentions an aggressive tumour that wrapped around the carotid. Unfortunately as this tumour continues to grow , it can and probably will, erode through the artery wall. This will cause a catastrophic haemorrhage. All that you can do should this occur is to have plenty of dark towels available to catch the blood. The most important thing you can do for your Mum should this occur is to just be there. To hold her, tell her you love her, stay calm and try not to panic. When this happens, it is quick and death is rapid.
My heart goes out to you Jackie.
Tammy