Scarlett, so very sorry that you are going through this. It is so hard and so painful, and so huge. It's your Mum. Nothing will make it any easier or better. It is awful, and it is the cycle of life.
I lost my wonderful Mum nine years ago to breast cancer, and she also died in a hospice with my Pop and me and my sister by her side. Pop was distraught. They had a very happy 53 year marriage.
The next year was so difficult. We were all so bereaved. She was also the glue of our family and was so loved. But we did carry on, and we did learn to put one foot in front of the other. I miss her terribly, but she had a wonderful, full and happy life, and she died an old lady.
Just be kind to yourself. Allow the feelings to be what they are, and also love the woman that she was. Support those around you that need supporting, but let yourself be supported too. Each day at a time, and always know that she loved you and wanted you to be happy.
She is frightened, and right now you need to strong for her, but the hospice will take very good care of her, and your loving care will carry her and make her safe. Now is the time to just simply be with her as much as you can. That is all you can do.
As ItCouldBeWorse said I also found it lovely to actually look after my Mum at the end.
Thinking of you, and all those that have lost their Mums. Please PM me if you need some support.