It would be nice to find out what the rules are on this. I know that both parties have to enter the marriage in good faith of keeping their marriage vows. If you can prove the other entered the marriage without planning to abide by the rules of the Catholic faith, you can receive an annulment.
If one is a non-Catholic they have to agree to allow the children to be raise in the Catholic faith. It does seem if the husband will not allow Terri to practice her faith by receiving Communion, this should be grounds for an annulment.
Maybe the parents need to check into the grounds for an annulment and specifically mention denying Terri her right to receive Communion.