J.C.
Good for you, S.- I really like that you both see the need to draw a line AND see that she may benefit from some flexibility. IMO - both are essential and the line you draw is pretty much up to you and your dh. So here are some ideas and please only use 'em if they seem to really fit.
You could ( if you choose to) make an ironclad rule that your bed is out of limits - and assure her that she can have a few ''sleeping on the coach'' nights - during the week. You could also say '''' it really is a problem when you wake me up at night -- so I'm going to put a blanket and pillow behind the coach- and you can go sleep there if you like''' You might offer an OCCASIONAL ''camp out ''' night where she gets to sleep in your room on a sleeping bag ( THAT IS ONLY IF YOU AND DH like the idea) --
Set your limits -- keep her needs in mind--- be flexible about most things so that the REALLY unbreakable rules have a better shot at being unbroken.
Blessings,
J.
aka- Old Mom