The
General Directory for Catechsis (para. 156) states that the lifestyle of the catechist must not be an obstacle to the journey of faith of their students.
Certainly, we are all sinners and DRE’s are not required to be sinless. However, there is a difference between being a sinner and publicly living a sinful
lifestyle. We all sin, but to live a sinful
lifestyle is basically living in a perpetual sate of sin with no indication that the person sees anything wrong with what they’re doing. Divorce and remarriage certainly fits this description and would be just such an obstacle (as would things like conhabitation, public support of things contrary to Church teaching [such as gay marriage], etc.).
Many parishes and dioceses actually have written guidleines stating that DREs and catechists can
not be living lifestyles that contradict Church teaching. Thus, anything like this would be grounds for dismissal. You might try contacting your diocesan office of religious education to see if this is the case in your diocese.
Now, all this being said, perhaps this DRE had a conversion
after her second marriage and
wants her current husband to get an anullment, but he refuses to do so (because he is an atheist). In this case, she would definitely be in a very difficult situation. It’s hard to know for sure (unless she tells you).
In any case, it seems like it would warrant a a call or letter to the pastor. At this point, I probably wouldn’t start campaigning for her dismissal, but I would just phrase it as an FYI, in-case-you-didn’t-know kind of thing (because it could be that they simply
don’t know).