User blog comment:IamJakuhoRaikoben/Chapter 373: Life or Death?, Review./@comment-24228963-20140228130013/@comment-7418318-20140228131535

The problem in this fight is that Mira, according to her own words in the GMG arc, isn't able (or willing) to use her full powers as long as someone other than the opponent is watching.

So Lisanna is already an obstacle just for being there and being conscious, even without Sayla using her as a puppet for fighting Mirajane.