No one can say whether this was a one time freakish thing or is going to be an ongoing issue.
One thing that IS certain is that the neighbor lady was very wrong to pick Maggie up the way she did. I'm rather surprised that she's dog savvy enough to understand that and yet did it anyway. That's a puzzler. Also, your son wasn't doing his job when he allowed it to happen. So . . . the humans in Maggie's life need to behave better, while also being vigilant about potential issues with Maggie (as they should be with any new dog). Yes, some dogs will put up with something like that w/o missing a beat. But I don't think Maggie's reaction was outside the realm of normal given what the lady did to her.