i feel like an ass

I work in a grocery store deli and there are only two of us that work the 12 to 9 closing shift. The other lady just called and asked me to work her shift bc her sisters husband is dying. I feel like the biggest ass for saying no but my baby shower is this evening!I told her I could work the majority of it if our boss would let me close early, since my shower is at 7. He said no, so now she has to work while a loved one passes away.