I think you're over assigning intent to her actions. In both of the examples I think you are referring to (since you didn't actually state them, I can only guess), when she "attacked" her sister in the ballroom, she was simply moving her arm in an exaggerated gesture to convey annoyance and frustration. Like any normal human being does when they are emotionally excited. Hell you can see Anna doing it multiple times in the same conversation. She's flailing her arms around all over while she's talking, it's called body language, and it helps convey her emotional investment in what she's saying. Well Elsa does the same thing, only for her, she can potentially shoot out ice. The other example being in the tower, when she freezes Anna's heart I guess? Again, it was an involuntary response to high emotion. The entire movie is built upon the idea of Elsa suppressing her powers, to NOT use them, to hide and conceal them. To say that she meant to hurl pointy spikes of ice at her sister in the midst of an emotional argument, and that she meant to again hurt her sister with that magic outburst is reaching I think. She never wanted to hurt anyone, that's why she ran away, that's why she told her sister to get away from her (a warning that Anna ignored I might add). Every action she took was to try and protect people from her powers, that she genuinely didn't have true control over. She knew she was a threat, and tried desperately to minimize that threat to the people around her. It didn't always work, but that's not the same thing as saying she's evil because she lost control a few times.
