Hmm, my only guess would be that maybe its locked because you don't have enough affection with her, due to how you answered at the beginning? You can gain affection with her every payment day by picking the choice that compliments her. I answered the 2-3 choices you have with her when you first meet correctly.(hearts came out) which may have made it easier to get her to give up her hair later. If this is infact the case I will update the log to include the intro days as well. (I will start a new game this weekend to test out this theory.)