Can not go into to fight her for fire school quest and I am a level 48 fire
Just because you have a quest from your Fire School professor, does not mean that you can automatically go to Mavra Flamewing's area. You must continue to follow the storyline in Dragonspyre, and eventually you will get the quest, "The Best Defense", that will take you to her.
This link shows all of the quests in Dragonspyre (Main, Side, Crafting, etc.):
You can scroll down to the Plaza of Conquests and see Mavra's quest, "The Best Defense". You can click on any quest for more details (like "prequests", "who" gives the quest, and "where" they are located, etc.).