I can understand you are struggling.  I am almost 64 now.  If I was in your Mum's situation I think I would just want you to spend some time with me really.  Taking time to talk about things you have enjoyed as Mum and daughter.  Asking her if there is anything you can do for her or anything maybe from her home she would like you to bring in.  She might like a little bit of soft music.  Is it just you or are there siblings you can talk with?. I am sure the Hospice nurses will understand and try to help.you.