Still have a hunch at this point that she was headed for Montreal from North Shore, MA.
I 93 to Concord NH, Then I 89 to Burlington, VT and on to Canada.
I'm guessing she took that route through Bradford, NH to avoid crossing over to VT at Lebanaon, NH. She could snake through on less traveled roads, then pick up I 91 in VT past Claremont. She could have snaked through VT, too, to get to 89 to Burlington a little further up then Lebanon.
Might have been road blocks or BOLO patrols in Lebanon.
Just guessing.