User blog comment:Omega natsu2/Chapter 364: Tartarus Arc, Part 1: Immorality and Sinners, Predictions./@comment-4999650-20131206150637/@comment-7418318-20131206185019

Just because she didn't have one particular take-over shape doesn't me she can't have aquired it in the meantime. And maybe she's just too shocked to act immediately.

I think it might be possible for Elfman going into a take-over to disrupt Sayla's controll over him. If she controlls him through his magic or his soul, "mixing" himself with a subjugated beast's soul and magic might throw off her shackels. If she controlls the muscles directly though, that would probably only worsen the situation by putting stronger muscles into her control and thus crush Lisanna's throat.