Have you asked him why he playes like he does? Maybe he likes to get killed? Are his characters all named Kenny?
From what he's said it sounds to me like she's just relatively inexperienced with the system.
For newcomers, particularly those who have played MMOs in the past, and particularly after hearing so many grognards comparing 4e with WoW, having a monster up in their face when they're not "the tank" is something to be avoided at all costs.
And a subsequent death may well be blamed on "the tank," because, in such systems, players expect the guy with the shield to absorb 100% of the damage, and tanks take 95% reduced damage from monsters, so to pose any threat the monsters essentially one-shot strikers.
That's nowhere close to how things work in D&D, but if she doesn't know that, it would explain why she runs away.
I played in a one-shot with some newcomers recently where as the first encounter we got ambushed in a marketplace, with the party rather spread out over a 30x30 grid. One of the new players was a good 15 squares away from the rest of us, and had a single minion adjacent to him, but was paralyzed with fear and repeatedly demanded that one of the defenders come save him.