I've been using Jyn in my arena team for quite a while now. I always use her rebel counterattack first when up against an autotaunter. Give the TM to SF or B2 and clear the taunt for wiggs to then kill main target. I do use stun batton first if no auto taunt. Usually on opposing Biggs just to slow down his attack.
Edit: my Jyn is 264 speed so goes first against pretty much every team I come across other than JE with droids and some super modded TFPs (or anyone under Zaul leader)
I am also interested though in what she does on D. I've always assumed whatever it is it's not optimum!