I know enough about production on The Bachelor to know that the producers tell the contestants whatever it takes - whatever - to get whatever the producers need out of contestants. I have heard too much insider info over the seasons. Forget about the reality.
My guess is that some sweet talker on the production end of the show 'splained it to Bristol in such a way that it sounded to Bristol like she had this wonderful opportunity to be on the show with all of these other wonderful ( think wonderful "human" - not wonderful competitive, cut-throat highly skilled, talented) contestants. In addition, she would be guaranteed she would be back with Mark who already knew and understood her. What did she think? Would she take a while and think over this fabulous opportunity?
Bristol is, of course, young, and I think is still basically fairly naive even with what she has already been through. If she had been a little older, she might could have weighed it out a little better, but I personally don't think she drew all of the right initial conclusions even though the rest of us could see it very plainly because I think she may has been initially fed a bit of a misleading bill of goods and was unable to see through it.
However, last night in that rehearsal clip Bristol looked like a lightbulb had popped on, and she looked miserable. She is now completely aware.
I felt like her routine with the chessboard, king, and queen fit the given creativity assignment, and she danced reasonably well. For her sake, I would hope that she could go out on a high note of dancing fairly well and of having completed her assignment well, but I would not be surprised if this did not happen.
I guess we will see...