I am so sorry that you have to go through this, the loss of a parent is so hard.
Based on what you told me, I have to agree with you that my original estimate was more in line with someone who's health was a bit better.
These things are hard to predict, but I would venture to say six weeks is more in line.
At this point I would discuss with her doctor if he feels Hospice would be appropriate. Here is some info related to Hospice and ask your doctor who he recommends:
http://www.hospicenet.org/