That makes as much sense as anything, I guess? Although the civilians she rounded up in that last scene in the city didn't really seem like a) the last holdouts or b) people who had already seen 90% of their friends and family slaughtered - I mean, at that point "I will kill people if you don't talk" no longer works as a threat. And she really didn't have time to kill anyone after that, unless she has, like, major area-effect death spells, in which case why bother with the fight on the bridge?

"Heimdall is lying to Thor and Loki" might explain it but I can't really see Heimdall doing that to that extent.

I can come up with half a dozen explanations but they all wind up working against the movie one way or another.