An understanding of the situation ...

Thanks to a beautifully clear explanation on www.religioustolerance.org, this has to do with mortal sin and salvation. When church rules are inconvenient, they are easily overlooked or bypassed. But the closer we get to the end of our days, the more important interpreting the rules correctly and doing it "right" is a matter literally of heaven or hell. After reading this, I can empathize with her fears that stem from her belief system.

[taken directly from the website referenced above]
The trap that some Catholics find themselves:

Couples that obtain a civil divorce and remarry without first obtaining an annulment are denied access to the Sacraments of Penance (a.k.a. Confession) and Holy Eucharist. (Catechism 1650).

They are caught between a rock and a hard place:

If they continue in the new marriage, then they cannot repent of and confess their sins through the Sacraments of Penance, and return to Communion. Meanwhile, their sins are accumulating. Because the church does not recognize their new marriage, it considers every sexual act within the marriage to be a new act of adultery -- a mortal sin. According to the church's teachings, this means that they will not attain Heaven when they die. They will end up being eternally tormented in Hell. There are only two ways of avoiding this state:

-To be fortunate enough to not die suddenly (e.g. to not die instantly in a car accident or from a massive heart attack). This way, they might be able to receive the Last Anointing by which their mortal sins are forgiven. Needless to say, this is a risky route to take.

-To make an "act of perfect contrition" instead of Confession. But this requires the individual to repent of what the Church considers their sins of adultery, and sincerely intend to never engage in "adultery" in the future.

If they separate from their new spouse, and live alone, and sincerely intend to remain separated unless a annulment is granted, then they can resume their access the Sacraments of Penance and Holy Eucharist. But that would require them to violate their new marriage vows, and terminate their marital relationship. This option often seems profoundly immoral to the couple, particularly if there are children involved.

Judging from the overwhelming percentage of Roman Catholics who never apply for an annulment, it would seem that most have abandoned their idea of mortal sin leading them to Hell. For those Catholics who believe in the teachings of their church, it would seem expedient to apply for an annulment as soon as possible so that they would be free to enter into a new relationship when they wish.