need title for party member

Hello everyone!

So, my bridal party is fairly small. My three sisters are all maids of honor and my FI's brother is the best man.

We are getting married in a small park, under 100 guests. Very short, simple, non-religious ceremony. No chairs, guests will be standing (except for a couple that can't stand for 15 minutes). I will also be hanging our rings in a small jewelry bag on a tree so that guests can touch and bless them as they enter the park.

We have asked FI's brother's fiancee (my future sister-in-law) to act as traffic/crowd control (telling people where to stand, giving directions), ensure that our music gets turned on in time and on the right song and most importantly- she is responsible for getting the rings off the tree just before the ceremony and giving them to best man and one of the MOHs.

What do we call her? I mean, I guess she's a groomsman or usher but that just doesn't seem the right title for her.  She will stand on the groom's side, because she's part of his family and it adds some balance, but I don't care if she wears a black dress (to match the guys) or a green dress (to match the MOHs). We really want to include her and this seems like a natural role for her but what is her "title"?

Obviously, we're a little off-beat. So a made-up title would be fantastic. I just can't think of anything and am looking for suggestions!

Thanks!