Why does my horse break into a canter when...?

alright, so i'm fairly new to horses(four/five yrs as a show groom) and since the horses i used to work with had no ground manners what so ever because they were 'show horses' and 'didn't need them' i have trouble differentiating between disrespect (subtle ques) and confusion. my horse has recently stated breaking into a canter when i ask her to walk at the lunge, and its difficult to slow her down because she just swings her away from me (i've never whipped her) to face me straight on. what the heck does that mean? is it defiance/bad training or confusion?