Bridesmaid Luncheon Ideas Needed

My husband's youngest sister is getting married in a year. Since she was in my wedding 9 years ago and attended a bridesmaid luncheon my sisters hosted for me she has wanted one similar.

I will be traveling to another state to host this event and will using my in-laws home.

There are a few themes I have come up with:

A Garden Party (which is pretty much what I had)
Champagne Brunch
Picnic
BBQ
Mexican Fiesta

I know these range in the formality, but I want it to be perfect for her and special.
Any ideas out there for possible themes?

I have read about the tradition of hiding charms in a cake and think I might just do something like that and since they are suppose to be hidden in a pink cake is perfect because that is my sister in laws favorite color.