Ummm... I honestly do not remember. This is totally why I should write things down, my brain tends to forget such things. xD I will come up with another power to be her third.

Lets see... What about saying the sisters were close when they were little but as they grew up, they started to drift and fight. I see Grace as the one to look for any other means besides violence to solve her problems while Elena's first instinct is to react violently. 

I think it would be more fun and would be a great plot twist.