Wedding plans and mother's illness?

My fianc�e and I have a wedding date of June 21 of this year. Her and I live in Los Angeles and my mother who is 82 lives in Kansas. Right after the first of this year, my mother got sick and went to the hospital and has been in the hospital now for a month. As soon as this occurred I left my job and came to be with her. I'm her only child. She's struggling with not wanting to eat and signs of dementia. My fianc�e is losing it because the time that I have been gone is affecting our wedding plans. She says that she understands my mother comes first however; this situation is affecting her life and is causing her to be unhappy which isn't fair to her. She says that she wishes that she would have found someone that had a healthy mother so she wouldn't have to deal with this. Am I being selfish in regards to my fianc�e's feelings and our wedding plans? Her life is involved in this too. I'd hate to leave and go back to LA with my mom in the hospital.