User blog comment:Carebearheart/Female Dragon Slayers/@comment-24277053-20150131002013/@comment-9595671-20150202133049

I've personally thought the reason Wendy doesn't experience it is because she can cast the Troia spell to cure it in the other slayers.

Kinda like knowing the spell had a side-effect of negating her motion sickness, its hard to really tell since so far only she and Cobra haven't been confirmed to have motion sickness. I'm pretty sure Cobra does have it due to how much stronger he was after the first timeskip, the issue is we haven't seen him in a situation where it would act up yet.