I Need Help With My Daughter`s Invitation????

My daughter is having her sweet 16 in January 2008. She wants me to ask for money as a gift in her invitations. She is having 150 guests. I don`t think it looks pretty to ask for money as a gift in any invitation. But then again, it is my opinion as a mom. What should I do. I want to respect her decision, after all it`s her party. She is my only child and she has everything. She doesn`t want any more clothe or anything else in her room. I was thinking of opening a gift registry at a store. But, they only do it for brides.Help!!! I need a lot of opinions out there. What should she ask for as a gift???? Help!! Thanks.....