Talk:My Past is Not Today/@comment-11677914-20150401191843/@comment-10390252-20150401203121

It tells me two things:

Firstly - Anyone who thinks that Sunset can't use magic in her human form has just been proven entirely wrong.

Secondly - Extreme emotion tends to cause unicorns to burst into flames (see Feeling Pinkie Keen).

If this is, in fact, a conscious spell-casting, then it is possible that this is a fire version of the water/air spell that Twilight used to give Rarity wings in Sonic Rainboom. Probably much more dangerous but 'dangerous and flashy' seems to be a key part of Sunset's personality, so we shouldn't be too surprised.