I agree, another example being Kakashi's chidori, that lighting is constantly hitting other parts of his body but he doesn't get electrocuted. I think it's because their elements prevent them from getting hurt by their own techniques.She's probably immune to it. Remember that her own acidic mist won't hurt her.
Hahaha! Nice one Broskie!^ No. Lava wont hurt Mei. She is already hot....!