Sharing the crib

V • After 14 months of struggle, had baby girl in 10/2015! So blessed...
So we will be having a lot of family staying at our house for our baby shower including my sister in law and her 2 1/2 year old daughter. I realized we have the crib already and could let her daughter sleep there. My DH immediately said no and wants to "save it" for the baby. They will be here for 1 week. This makes no sense to me...thoughts?