Hi Nette, I'm sorry for the position you and your Mom are in. I went through the exact same thing with both my Mom and Dad. It's one of the hardest things to do you will ever do. I have been diagnosed three times with cancer myself and have said several times that taking care of both Mom and Dad in Hospice was the hardest thing I could ever do.
What can you do? Just take care of her like she took care of you when you were a baby. We are there for them now, it's our duty to be sure they have everything they need. Our positions have switched now and you can just be sure that she has the simple things to make her comfortable, keep her warm when she needs it, but don't think anything about it if she kicks the covers off. Give her water when she will take it. Ask the hospice nurses to explain the process of a person in their final days and this will help you. It helped me. Both Mom and Dad died peacefully and quietly and it was a much easier process than I thought it would be. Ask your Hospice nurses about anything you may have questions about, and you can also ask @carm any questions on this site, just click on her name to go to her page and ask what you need. She has been an end of life nurse for several years and can answer most any question.
One day you will look back and feel proud that you were there to take care of her in her final days. That may seem strange, but you will understand one day. I wish you the best.