I never gave either of my littles a lavalier as ordering jewellery from the States is quite expensive and the only option at the moment.
Possible ideas off the top of my head:
1. Attaching it to the paws of an angel bear
2. Tying it to a wine carnation
3. Placing it inside a picture frame that you painted yourself
4. Including it in the pages of a home-made sisterhood scrapbook
5. Hide it in a bag full of candy (in a box of course!)
6. Write her a poem and attach the lavalier to the paper
7. Order a balloon delivery to her dorm room/house room and have the lavalier inside one of the balloons. Include a note telling her that it's inside so she knows to look for it.
That's all I can think of for now.