Up until the civil war lead by Thrima and Lilja, Grimhild had been a seer, one with the very rare ability to see into he future. Once the war broke out, she was part of the make-shift council that was formed after the warriors and priestesses who refused to fight retreated to Hlidskjalf. She wanted to immediately take a group down the mountain to negotiate peace but after sending scouts to get an idea of the breadth of the conflict, it was decided that both sides were too far gone to talk down and those at Hlidskjalf did not have nearly enough trained warriors to try and stop them by force. They had to bide their time. And so they did until Grimhild had one of her visions.
Ever since Raven killed the frost dragon king, the number of dragons dropped dramatically then they nearly vanished altogether when Raven herself vanished. After ten years of civil war, Grimhild had a vision of the frost dragons returning in full force and completely wiping out all Valkyrie kind. She could not wait to intervene any longer. She went down the mountain to warn the two warring parties. In short, the priestesses at Sesrimnir believed her but most of the warriors across the valley did not. When the attack did come Sesrimnir was saved but the warrior's fortress, and all those there were wiped out. More than a year later Grimhild was named queen. Most of her 82 year reign was spent rebuilding.