Kristen, it is a very interesting question, and I've been looking for recent research on the matter myself. I haven't found solid evidence yet, but I suspect there is a relationship between long term use of antidepressants and mood instability.
I have also seen a lot of negative sentiment towards the use of antidepressants for children in the literature, and warnings about the suicide risks for some people when taking antidepressants.

One of the difficulties with asserting that the bipolar disorder was brought on by the use of antidepressants is that unstabilised Bipolar is known to have a tendency to grow in severity over time. That could mean that you and I had depressive symptoms which we first noticed, and only later did the severity of our Bipolar reach the point when mania became troublesome.
We can't be sure whether the antidepressants influenced that or not.
Studies would need to account for that somehow.

Peter