MG, you've really been outdoing yourself lately. I'd suggest maybe something cute like that hot redhead Angela's first messygirl shoot with the button down shirt and crew socks. Or play off her fitness model vibe with something sporty. Either way, some nice cool whip pies to get her started (so she's got something yummy to taste), followed by green or blue slime, chocolate (since what pretty lady doesn't love chocolate), and more pies. Ask her about her first messygirl experience afterwards. Just my two cents...
Give her the full messygirl initiation while wearing jeans and either Keds of Converse without socks. Have however is getting her messy fill a sneaker with chocolate and make her drink it.
I know everyone has their own tastes in wam, but I was surprised at many of the replies that dealt with what to do to her face and hair.
Here we have a fitness model's body to mess up. This excites me. Let's see it, perhaps starting with anything clingy when wet, then gunge her so that the fabric sticks to every curve, until she goes nude or at least down to a g string.
So yes, mess her from head to toe, hair and face included. Hopefully she likes the feeling and writhes around in the mess for awhile.