I would not assume. I would wait for DS to tell me directly. I once assumed something and was totally wrong. Wait for him to ask you (for a ride or weather she could come over etc.)
Your are right, if he doesn't ask, I'm certainly not going to bring it up. But I wanted to have some sense of the issues so I didn't start sputtering or agreeing to something and then changing my mind later if/when he does ask.
The no girls in boy's bedrooms makes sense and is the rule I was raised with. It's weird, though, because DS has had so many female friends in his pre-adolescent life (and still does) that have been just like his male friends and have full run of the house. Now, of course, that will change. It's going to be a hard rule to make and enforce. Also, there is the issue of the rules at her house. I am planning to chat with GF's mom and compare notes and rules before any get-together.
Thanks for the help.
