welcome to HCM;
I guess you understand that your mother is in very advanced stage of her cancer.In this stage she can have multitude of problem all over body.
It is very important that she gets required pain medication so that she is pain free and other drugs for her problem like constipation
,swelling of body.It is called palliative treatment and is very important to improve quality of her life .
Regarding time it is very difficult to predict but the time fram is usually in months.