I completely understand this. I feel the same way with many of my friends too. I never thought about my (crappy) boundaries being the issue - I always assumed it's because I get so caught up in pretending. I pretend that everything's fine and then feel hurt when noone notices that it's not.
So I guess I need less boundaries is some ways and more in another.

I promise I'm not trying to be negative...but are you sure she doesn't realise that she's hurting you? It's just hard for me to imagine constantly complaining to someone who I KNOW suffers from a sleep disorder about being tired.