I really like how your colors and your lines turned out. The red background really does contrast well with the greys and blues. That metallic look on the wand is also fantastic as well as your shading. The fire design is a very good length as well.
Now for the things you should do: First, a little more space should be set between the two. It looks like they are fighting at about... 5-7 feet apart. Sacrificing some of the cape wouldn't be too bad for giving emphasis to the shot. Second, that summoning pose seems off. The hands should be facing in towards the energy as if they were containing the heat and power before firing it at her opponent. Her stance can also be lowered to emphasize her anger and effort of using her magic, leaning forward more.
I'm probably not as good of an artist as you, but I hope this critique helps. ^^