From what I understand, elemental magic is one of those things one tends to have or not have a natural talent for- a bit like the way some people have a natural talent for singing but others can't carry a tune in a bucket. One can refine one's talent with practice, but the time and effort may not always be best spent there.

People tend to have an affinity for a particular element- fire or water or air, and so on- and might not have much of a knack for elemental magic in general. I can do a little bit of earth magic, but it was never much, and I've no skill with fire magic at all. Focusing on purple magic made more sense, since it came more naturally to me.

[Hence why she keeps using a flint and tinder set to make cooking fires, instead of starting them magically.]