Was seeing a girl for about a month of two who text me this morning saying we should just be mates.
So I'm pretty gutted, but boo hoo hoo. I'm not going to let her wussify me.

We've both agreed to meet up today to see eachother as mates and talk about stuff.

My question is; How should I act with her?

I could pretend I don't care, but I am pretty gutted and I want to have a moan at her for stringing me along I guess.
Also, I wouldn't mind turning her into a booty call, but is this possible after the; "let's just be friends" - break up?

yes, it is possible to make it a booty call

before you meet with her, get your priorities straight of what exactly you want to get out of your relationship with her

if you wanna let her have it, then go ahead, but don't expect to get along with her later, especially with booty calls.

it's okay to be gutted about it, but DON'T act boo-hooey, and DON'T be malicous toward her. Just let her know that, yeah, it wasn't working out, I like you a lot but we're just too differnet to be Romeo and Juliet, then you might be able to bag a booty call

in short. don't act too affected. don't be confrontational and don't initiate contact with her too soon thereafter and you may have some fun later

good luck