I would reply back with a comment of "That sounds great! We really appreciate you and DH's Dad understanding the dangers of traveling in the middle of the winter" and than send it to her, DH, and his Dad...
It would seem compromise to me would mean since you travelled all the way last year, they could travel all the way this year not you meet them half way.
My kids love gift cards too because they get to choose what they want. We always try to hold them off until the clearance sales start so they get more for their money.
Let her know those are great and as pp said maybe invite them down to stay if that is feasible.
I somehow missed this thread the first time around. Good job standing your ground Missy. Some people are just difficult, and there is no way around it. Sounds like it is her problem, not yours!
I hope you sent her a great big ole email telling her how much you enjoyed the gift cards and maybe suggest doing the same thing again next year (passive aggressive is as passive aggressive does--KWIM?)