I can imagine how you feel - work is a place where you can be yourself and forget about the stress of having been a JW. Now there is a possibility that there is going to be an awkward situation and the focus could be on you.
I think you need to look at this differently though. If there is a shunning event, she will be the one to look silly. If it gets talked about, you won't be the bad guy. Everyone will be feeling sorry for you. And while no-one likes to talk about religion, they do love to talk about stupid religious practices such as shunning.
In a previous job, half the people I worked with were related to JWs (it was a very small office). They were constantly gossiping about the crazy things that happen. I never let on that I used to be one and I didn't take part in the conversations either. But it did give me an insight into how non-JWs feel. They sympathized greatly with the exiting and out of favour JWs in the family and had no tolerance for the narrowminded attitudes of their witness relatives.
Most people prefer to blend in so maybe the JW at your workplace is "broadminded" (she is after all playing sport, which is unusual). Shunning is such an obviously stupid practice - I can't imagine anyone putting it into practice at work, but you never know!
Hope it works out.
penny2