You have to do this casually.

Don't make a big deal about it just express your desire for her to attend.

If she says no one will talk to me. Say something like what am I chopped liver?

Say we will go and make fun of all of them.

Come on man be creative.

I would not fret to much about it but some friendly pressure may make it worth your while.

Just make sure she understands you really want her there for no other reason than you want her there.

Relax
Eat
Think
Act normal
React.. Smartly.
Do something different.
Emulate.
Do Work.

Lets get "RETARDED" in here.