He could have. And she would have tried to fight her way past the guards, the same as Cas would have done--and probably made a bigger mess for everyone involved. Or she could have knocked herself out and tried to meet him in his dreams.
But that was then. Now, she really could be there for him at a moment's notice, to sit up with him, and brew the dreamless sleep potion when things got rough. "I could stay here," she offered, "If if would help. I'm used to camping under the stars; I can sleep anywhere."