Lying naked while the snow falls all around me
Drifting closer to the edge but she won't help me
Wake up in sweat
Full of regret
Try to forget

At the begining of these lines, I don't think she has begun her transformation yet, but is right there at the final step and if she takes that last step there will be no turning back. She wants Halone to step in and help her people, but Halone does nothing and Iceheart goes over the edge.

The last of these 3 lines Iceheart has become Shiva, she wakes up in sweat signifying that even the bitter cold of Coerthas isn't enough to chill The Ice Queen, confirming her transformation. Her regret, I am thinking maybe her people had sacrificed themselves, or maybe even tempered themselves, in order to summon shiva through Iceheart and now that Iceheart can't turn back she doesn't feel the sacrifice was worth it. Trying to forget, This might signify that she can't control the embodiment of Shiva, this may also tie in with her regret, if she can't control the manifestation of Shiva then she will surely regret having summoned her. I think the last 3 lines confirm the fact that Shiva was just too much for her to control and she has lost herself entirely.

A lot if this is basically along the lines of what you have stated, just with a little tweaking or clarification. Again that's if these are the correct lyrics to the song, but I have very little to go on and these interpretations are all we have to go off for now, We don't have much longer to learn the truth though! Until then it is fun to speculate.