When she headed to Outland, at level 60, Aeven had died a total of 60 times. About once per level, on average.
When she headed to Northrend, at level 70, Aeven had died a total of 139 times - minus the 60 deaths in the Old World, that means she died 79 times in Outland. About 8 times per level, on average.
She's managed to get about 10% of a level completed in Howling Fjord so far, and died once. So, it looks like Northrend is going to be (hopefully!) about on par with Outland in terms of difficulty.