Reddit mentions of Annulment, the Wedding That Was: How the Church Can Declare a Marriage Null

Annulment law is among the most detailed and complicated. I recommend the book Annulment, the Wedding That Was: How the Church Can Declare a Marriage Null to anyone looking for a faith and in-depth explanation of the meaning & process of annulment.

Divorce isn't a sin for Catholics, unless I suppose done frivolously. Which wasn't the case. It's the remarriage without an annulment that's a sin- which seems to be a possibility.

A civil divorce doesn't have any standing to a marriage. Tell them to speak to a priest about starting the annulment process. Since she's still married to her first husband until proven otherwise, they'd have to live as brother and sister (no sex basically) until the decree of nullity is granted, and then speak about getting their marriage convalidated because they aren't validly married.

Though the annulment may not be granted, in whichcase she's still married to her first husband. An invalid marriage is decided by anything 'wrong' that happened at the time of the vows- lying, under pressure, Catholics marrying outside of the Church, or to non-Catholics, without dispensation, etc.

If all of that was fine, even if he turns into an asshole later, they're still married until death. But, in such cases, the Church is fine with civil divorce to protect yourself and any children.

It's complicated and such. Again, ask them to speak with a priest and get it all sorted. This book may help too - http://www.amazon.com/Annulment-Wedding-Church-Declare-Marriage/dp/0809138441

EDIT: If she really isn't allowed back in her Church, that shouldn't be condoned. But she may have to refrain from taking Communion until she goes to Confession. That's all presuming they didn't all do everything I just typed up already, in which case she's fine and the parishioners are doing it wrong.