Someone posted that you shouldn't give something that is a big reminder of her loss. Don't worry about that. Everyday she wakes up and doesn't see Daddy will be a reminder that he is gone.
Skip the flowers. They will get so many that it is overwhelming and then they die. Plants are better but if the mom isn't up to watering or replanting, they too will die. I like the restaurant gift cards idea.
Being a busy season, have the troop plan things that will help out the family: including the girl in a cookie baking day, taking a group trip at night to see Christmas lit houses, having each family make a meal (make a calendar of what others are bringing and what the family likes and put in foil pans to be frozen if desired), making individual cards, etc. Teach the girls that it is all about finding what would be helpful and being there for others in a time of tragedy.
Bless you for wanting to help.