As someone who has been through her fair share of friendships, I'd say that keeping a distance from this girl isn't a bad idea. She doesn't seem to need you until she "needs" you, and you are the one who winds up getting hurt because of it. From what I've read, this sheltered friend, as you've called her, doesn't understand how to handle relationships.

Someone above mentioned that you guys discuss boundaries, and I agree. I have heard more than what I've ever wanted to hear from my SIL about my brother, and I don't need to know that stuff.

Be careful, tread lightly, and keep standing up for yourself. Sometimes when people get mad it's because you called them out on their behavior. Let's see if she "gets" it.

Good luck!