The marriage was not sacramental, however the contract was (I'm assuming) valid = you must assume the marriage was valid and your daughter is still married.......if so, your daughter is not free to marry again - but ya gotta talk to a priest, hopefully a traditional one. Waste of time to talk to a NO one.
Annulment means the marriage never happened, no way to know from here but sounds like the marriage, while not sacramental, was still a valid marriage.
The traditional priest will best determine if the marriage can be annulled due to the direment impediment of disparity of cult, or if a dispensation can be applied to that situation.............if the couple had children together, then it would be pretty hard to see how the marriage could be annulled.
If you look at it from the Church's position.......... the Church, as the only protector of the Sacraments must, initially at least, side with the Sacrament. IOW, the Church initially assumes that pretty much all marriages are valid, whether Sacramental or not, for the sake of the Sacrament, or in this case, the matrimonial contract.
No way around it, ya gotta see what the traditional priest says when it comes to annulments