Mom won't look for someone to help her care for my dying father. What to do?

My father is just starting to start hospice as he is nearing the end of his battle with cancer.  Dad is at home with Mom taking care of him.  she is 82 and I can't convince her to get help at night.  She expects me to help her change my father's diapers and I am uncomfortable with this.  It takes us over an hour to do so.  I can't convince her to get help...she just wants me to do it.  What to do?