you could also try and find her 'triggers' for what wears her out the most--play dates with other dogs, fetch in the backyard, car rides, etc. We had this problem with our dog and it was actually solved when we dog-sat for another dog. Our's didn't want to sleep with us because he wanted to know what the dog crated downstairs was doing so he preferred his crate to being with us...and we haevn't been dogsitting for a few weeks now and he is fine in his crate downstairs now.

Sometimes it's just luck!

(I'm just a dog owner and absolutely no expert )