I totally didn't see that coming...at all. Excellent.
This chapter also really made me like Lothiriel's character (and Eomer's too). Lothiriel doesn't seem like the type of person who is easily cowed, but I wonder if she would be as arguementative if she knew of his higher rank; she also doesn't seem to have noticed the fact that he addresses her by her name, which seems a bit familiar to me... even if he is a king. But that seems like such an "Eomer" thing to do, especially with the way you usually characterize him. : )
Their banter is fantastic, by the way. I love Lothiriel's logic: "Well, you shouldn't go to sleep in my brother's tent then, should you." Serves him right then, in my opinion.
Best line(s) of all: "I can guarantee you that the King of Rohan won't be interested in marrying you after this escapade. You may have my word on that." --if only she knew!
I can't wait to see how this unfolds.