What she just walked it ??
What if you or your husband had been naked.. just got out of the shower... whatever..
That's just rude !

If you are uncomfortable confronting her you can just lock your door.. or even have a sign on the door that says to knock before coming in.

Some people!
I don't have that issue with the parents . but the grandparents.
When ever they come to pick upi the kids they always try the door without knocking and each time I tell them they must knock as it will NEVER be unlocked for security purposes.