20 years worth of baptisms invalidated

My wife is a "former Catholic" (not sure if this is a valid description) that currently attends a Baptist church with me. She still holds on to many of the traditions of the Catholic church. I am open (and many times agree) with many of the Catholic beliefs.
She once worried about not taking The Lord's Supper (Communion) enough (our church observes it at least once per month) and whether Transubstantiation occurs. What is the Catholic stance on this? Does the sacrament have to be performed by a priest? Some Baptist believers believe that the husband is the priest of his family. IMO, I suggested that if the Lord turns the wine to blood, then wouldn't it happen, even if the pastor does not necessarily believe in the transformation? Does it actually take his (priest or pastor) belief for it to occur? Or is it up to the faith of the believer? Or does God cause the change?

Just wouldn't mind hearing your (and others') opinion on this....
Brennan can speak to this more specifically but it is my understanding that both thought and action are necessary for the transubstantiation to occur