User blog comment:SoulRise99/Sage Dragon Slayer Magic?!/@comment-1776824-20170222003110/@comment-7418318-20170303135617

Wendy was badly hurt and lacks the ability to heal herself.

In her current bad state she won't last five seconds if Acnologia wants to kill her quickly. But then back on Tenrou he did play around with his prey for quite some time, so maybe she'll be able to survive for some time.

Hmm... thinking about that... he did play with them even though there were 2 real and one artificial Dragon Slayers present, but blitzed Serena. I wonder if he just wasn't in the mood for games with Serena, or if he considered Serena to be an actual threat and thus dealt with him right away instead of playing.