The wife's destination is with the States. Also she is a resident, and the credit card that was used to pay was issued in the States so I think Amercan law should apply.
From
http://airconsumer.ost.dot.gov/publications/delays.htm
If your flight is canceled, most airlines will rebook you on their next flight to your destination on which space is available, at no additional charge. If this involves a significant delay, find out if another carrier has seats and ask the first airline to endorse your ticket to that carrier.
I think two extra days it's a significand delay
As LOT guys say LOT has "own internal" rules that are not public and everybody agrees with them buying a ticket. That "rules" deny flight changing if the ticket is not-transferable.
But nor me neither my wife heve ever seen/heard about that "rulles" before the flight cancellation.