Should I let my daughters girlfriend stay overnight?
It's up to you but I would say go with your heart. Do you want her friend stay overnight?
Not in a million years! It has taken me quite a long time to be this lenient.
It is okay for parents to set boundaries for their children to follow but it is also important to let them develop normally and date. You have to be careful that your boundaries don't stifle them.
You are just being too lenient with them.
Maybe I am, but that doesn't mean I'm wrong, and it doesn't mean you're wrong either. I guess we just have different styles of parenting. To be fair, I was just like you before, and it took me quite awhile to open up and trust my kid's decision, so I believe you will come to realize it soon enough.