a friend of mine is planning for her DH's 40th birthday right now. He didn't want a party so instead she's going to give him 40 gifts all about "40". I'm not suggesting you give your DD 40 gifts, but here are some ideas she is using:
40 birthday cards - She sent an email to friends and family asking them mail him b-day cards. She's keeping this a surprise by having them delivered to a neighbor.
40 balloons
$40 gift card to his favorite store/restaurant
40 special family photos in a new scrapbook
40 minutes of one-on-one basketball in the driveway
40 notes, each saying one thing she loves, admires, respects, . . . about him
"40" snack jar - similar to trail mix (ie. 40 of each: M&M's, peanuts, marshmallows, raisins, pretzels, etc.)
And her list goes on, but that's all I can remember for now. She's trying to stay budget conscious and many of these ideas are free or cost very little.
Good luck with finding what's just right for your daughter. I'm sure whatever you do will be very special to her.
:-D