I am so sorry you are at the stage where you are writing questions such as these. I do know though it must be natural as I too wondered the same things with my mother.
I am not a professional by any means but, from what you describe the end is approaching to your mother's battle. There are signs you can watch for. Signs you may want to be aware of in order to be more prepared. I would ask your Hospice help to suggest any literature they may have or know of. I looked over some books while in the hospital with my mother the last few days she was alive. They were about the last stages before death and some had more in depth looks at death too. Like some peoples personal experiences with a loved ones dying. I never ever imagined I would have read a book or books like that but, when my mom's time was coming to an end I needed to be informed.
Please know you and your mother are in my thoughts and prayers.