Kay, how about a pic of Jill on a card, either via the computer or even just scotch-taping it to an 8x10 sheet of paper and a message to Dad to let him know that his little girl is thinking of him, where she is, letting him know that she is very much alive in his heart.
I've even pulled out a card from previous BD's and other dates, and they were always very much appreciated. Just a thought, since you asked if you should 'let it slide'!
I believe we should do everything (that we are emotionally able to do) to keep their memory alive...keeping them with us, always.
Your husband will be in my thoughts and prayers, missing his girls so very much.
Big Hug and My Love to you Kay,
Terry