Sadly the anti-matter/matter exchange would be disastrous. Any encounter between particles and antiparticles, in this case the highly charged energy particles that constitute the fire breath and an equal amount of anti- fire breath particles leads to the annihilation of both, giving rise to varying proportions of high-energy photons (gamma rays), neutrinos, and lower-mass particle–antiparticle pairs.The resultant explosion could very well lead to Evvie's own demise in a flash of energy rivaling the big bang. Something I doubt Evvie could handle even as a demi-god.

Again as I said if someone were inclined to make such an area and want to have others participate in it, there would by virtue of the concepts of role-playing, have to be a way to meaningfully interact in such an environment otherwise it would be a moot in terms of multiversal exchange.