Excuse Letter in Missing Night Shift for Christmas

Dear Supervisor,

I am missing my shift tonight to spend Christmas with my family.
I am filing the proper leaves and my team mate Shelby will fill in for my shift. I will in turn take in the New Year shift for her, if you allow it. I'm sorry if this was such a unprecedented decision, but my mother has really asked me to be home for the holidays- as you know she is very ill and this time is very important in her recovery.

Thank you very much

Merry Christmas
Elaine