Maybe she would like to take a trip later, after everything has settled down. She will have so much to do to get the estate settled and all. There are usually so many people around immediately after a death. After a few weeks or maybe a month, everyone else goes back to their lives and you are left with your grief. I would send her a card and flowers or chocolate or whatever you know soothes her soul and suggest that the two of you take a roadtrip, cruise, etc at a later date.
I know that this was expected, but it certainly doesn't make it any easier.