What’s her contention? That the angels arrived too late to actually guard the people while they were still alive, so they contented themselves with guarding the wreckage? Guarding it from what exactly? Were the angels there to shoot looters?
I believe the first few days after the attacks, there still were many questions in the minds of family members and loved ones regarding the events which had transpired and the location of their loved ones.
I wouldn’t be surprised if multiple prayers were sent out worldwide for a legion of angels to watch over loved ones until events were under control.
We also know that some territorial angels, though dispatched, might be hindered by adversarial spiritual domains and might not have arrived until too late, simply posted until further directed by legitimate authority.
Such are plausible explanations, but neither have adequate information to suggest they are the legitimate explanation for their presence, as it might not be any of our business.
If the report is true, then some reason for the occurrence fits in His Plan.
Medieval Christians believed--on a person's death bed, angels and demons competed with each other to try to either inspire, or tempt, a dying person--to either escort their soul to Heaven, or drag them to Hell. Yes, this is scary stuff, but so is death.
Such an situation is hinted at even in the bible...with the reference to a dispute of the angel Michael and the devil over the body of Moses (Jude 1:9)
Certain near-death experiences in modern times have tended to correspond with such a view too...
As a Christian who does accept the biblical description of angels, I see no reason to doubt what she said she saw--even if she's now not a practicing Christian, as the bible never teaches that only devout Christians can ever perceive angels.
The idea of angels somehow "failing" as guardians too is just dumb--in that EVERYONE in the providence of God has a time to die.
That angels would be standing in rank, around a horrendous death scene immediately afterwards--doesn't contradict biblical and historical Christianity one bit...