Dismantling the guest bedroom sounds like a great idea. With your close friend who crashes for the night, could you simply be honest with her about needing space? I hope she doesn't ask to crash on your couch if you get rid of the bed!

Someone inviting themselves to stay at your house for the weekend is already way outside the good etiquette lines. I would just tell them no. "Sorry, we can't do that." I've used that line (or the variant "Sorry, I can't have house guests.") many times and no one has asked me to elaborate.

What I've found is that quite a few other people also dislike having house guests and no one has gotten upset with me for not hosting them.