My wife took two exedrin migraine and continued breastfeeding. Is this something we should worry about?

Avoid aspirin. Although it likely did no harm, I would not recommend breastfeeding when aspirin has been ingested. Aspirin and compounds like it (salicylates) should be avoided in children because of the risk of Reye Syndrome.
Don't make habitual. Once in a great while shouldn't hurt but remember Excedrin migraine has more caffeine that a baby may care to have. Not so much worried about the aspirin component once the baby's born...but it can still do stuff to the baby as it matures if taken too frequently. Your OB/GYN can guide you a bit more fully.
Probably not. As a one-time exposure, there should not be any problems. The aspirin in the Excedrine Migraine can cause problems if she continues to take.
Do not fret. A couple Excedrin pills will be very unlikely to cause any transient or lasting problems. If she continues to have migraine events while breast-feeding, suggest using an OTC preventative such as riboflavin, butterbur, Co-Q10.