unfortunately, it all depends on the viewpoint of the Church that she belongs to.
These days in most Protestant churches, they will accept previous divorces before either of you came to Christ as repented from, and thus forgiven by God. (see Oscarr's posts above)
But in the Catholic Church, it's a different story.
There are cases where a previous marriage can be annulled by the Catholic Church, based on the life circumstances that were present before the marriage happened.
Previously unknown sterility for either a man or a woman would be one of these conditions.
Those circumstances (had they been known at the time) would have disqualified either herself or her husband from making a life long commitment had a priest learned of the pre-existing prohibitive conditions.
But if the prohibitive conditions developed after the marriage took place and the couple were married by a priest in the Church, then they are both usually stuck for life to each other, until one of them dies.
So yes, they could easily get a civil divorce, and then marry again in most Protestant churches.
But as far as the Catholic Church is concerned, they can't marry until all the previous spouses die, and the pre-existing conditions (as they pertain to the bride) are removed.
An example of that would be if she had been sterile before the two previous marriages, but now she is past menopause. In those conditions she could marry.
The one exception to that would be if they agree to a "Josephite" marriage, like Joseph and Mary had. That's where the couple lives together, but without any conjugal relations, and sleeps separately, no touching or embracing, etc.
As you can imagine, that's a very difficult situation to endure.