User blog comment:FairyRaven/Fairy Tail Chapter 437: Magnolia, Review and Commentary/@comment-7418318-20150525093151/@comment-7418318-20150526071607

I think poison magic isn't such an obvious choice for her after all, at least not intentionally learning it.

In the manga we have no indication that she remembers her past as a snake and in the anime the memories that bled through were rather traumatic for her.

So in the manga she wouldn't have a reason to go for poison, unless it's a subconscious thing, and in the anime the same might be true or she might even avoid the subject.