Have them get marriage “counseling” to be sure they ask and discuss the hard questions. Maybe one of those in-depth questionnaires they can do together to see how each feels about money, finances, budgeting, chores and gender roles, children or no children, how many, expectations for kids, discipline, experience with kids previously—the reality is often far different from the expectation! If they foresee children, have them babysit someone’s child/children for a night and then maybe a weekend. Everyone pictures kisses and cuddles vs screaming, back-talk, sneakiness or kids who hate being affectionate.
What are their personal and professional goals in life, what are deal breakers, how much togetherness is too much or too little, what is an ideal vacation: time with extended family, extravagant national or international getaways, historic reenacting, major cities vs. wide open spaces, amusement parks, historic sites, lots of cultural events or decompressing on a beach, camping, staycations, or “what’s a vacation”?
Do they have similar spiritual beliefs? What happens if one becomes disabled? How will they divide time between families? What are their holiday traditions and how will they mesh?
What religious training does each foresee for kids? What does each think about porn, sex toys, fantasies or kinkiness? What are each looking for from marriage?
When does each want to retire & what would that look like? Moving or staying in the same place forever? Downsizing vs. buying a big place to host lots of family? World travel? RVing? Quiet life in a warm climate/beach or living next door to grandkids? Working until you die, starting a family business? Having a more fun career?
What role and authority do grandparents, aunts & uncles, friends have? How much time spent with friends vs at home is too much? What is OK & not OK to do apart from each other, like drinks, bowling, strip clubs, gambling, weekend trips with bros/girls vs. week-long ones? How does each use vacation time? What constitutes slacking and workaholism?
How clean is a clean house, with and without kids? How does each person deal with stress and conflict? Scream it out and be done, go to their caves and think about it? Discuss situations daily or weekly to pre-empt conflict? What happened when their parents/guardians disagreed, how did they resolve it (or not), and what would they do differently?
Encourage them to discuss the hard questions now. Doesn’t mean neither will change their mind later or behave differently in the heat of the moment, but so often we make assumptions and then the reality is far different. Maybe encourage them to do Myers-Briggs testing as a place to start discussion. I’m sure there are many books on the subject, some religious leaders offer marriage preparation, etc. Best to reserve judgment on her decisions, but do ask lots of questions and be there to listen to her uninterrupted.