That is so sad! But what's even sadder is that this whole thing is repeated over and over again. How many people get disfellowshipped each year because they are weak but not wicked. The whole disfellowshipping thing is wrong on so many levels.
As believing witnesses we were all guilty of perpetuating this obscene practice by going along with the shunning part of it. I think we all can look back and regret treating disfellowshipped ones badly because we were doing what we thought was right at the time.
Please don't beat yourself up too badly for this. I agree with the other poster, if you can track this girl down and apologize it would be good.