MIL Rant

My MIL always askes if my daugter can sleep with her when she spends the night at our house. I don't know why she want our baby to sleep with her when she has a perfectly good crib that she loves! My daugter is now 2 and sleeps VERY well at night. Maybe someday when my daugter understands it's a special treat to sleep with her grandmother then yes. But for now, I put my foot down and say no for many reason. First of all, I find it a little werid and I don't understand the obsession with wanting to sleep with my child. Second, my daugter loves her crib and probably wouldn't get a good night sleep with her, and vise versa. Third, I don't want to mess up her routine unnecessarily and have my child wonder why she can't sleep with mommy and daddy. What are your thoughts? TIA!