I would rather her wear pjs to bed but I'm not going to fight her about it as long as she is wearing something to bed. I do make her wear elastic wast bands at least, no zipper and button pants.
This has turned out to be a kind of good thing though. She puts regular clothes on at night and wakes up dressed. No more fights about getting dressed in the morning! I'm not sure if she has thought this through or not but she made a comment the other day that made me think she has. I said "I need to go get dressed, and then we can go". She looked down at her body and said "I'm already dressed!".
As far as I'm concerned she can wear regular clothes to bed for as long as she wants.