Continuity mistake: Before Kara uses her heat vision against Vartox she gets some dust on her suit, then she stands up and the dust is gone.
Continuity mistake: When Vartox starts to fight Kara the sun changes between shots.
Continuity mistake: When Vartox attacks Kara from behind the background changes in the next shot.
Answer: Another part of why the change was that it's cold in Canada in the winter and the old costume didn't protect her from it, whereas the new one is nice and warm.