Funny, I asked that same thing about a year ago about NW. I called them and they said no too. Perhaps because it was your deceased husband, it was an easier "Yes".
They told me that with parents, there might be other heirs, (lame, but I can see that there might be the possibility of conflict).

Well, someone suggested that I keep posting miles to the account until I have enough for a rewards ticket (she had about 15,000 miles).

Meanwhile, I managed to get her ff number and set up a log-in using my own password, so I do have access to the account.

Good luck.
Rita