She is a former private-school student who had challenging classes and not much extra time. Now she has a much freer schedule and, with one exception, doesn't seem to be passionate about her classes.
How do we ensure that she take school seriously, although her schedule is light?
I would be pleased that your daughter is "passionate" about even one of her courses. I have met very few college freshmen who are thrilled about all their first semester courses. Her passion about her courses is not the best barometer with which to measure the worth and value of these courses. She may not want to divulge much to you about her courses because she considers herself a college student now and part of her being a "grown-up" college student is her not needing to "report in" to her parents about her new independent adult life.
If she is attending junior college and still living at home with you, it may be harder to convince herself that her new independent life has really begun. It may not feel that different than high school in many areas. Her schedule is light because she is not taking a full course load. Was your daughter disappointed at taking only three courses? It's possible that she might be relieved to have a schedule that is not as consuming as it was in private school.
I think it would be good to have some open-ended, non-blaming, non-pressured discussions with her about your expectations of college life for her and her own expectations of college life. They may differ and you may already be communicating to her that she is not living up to the high standards of academic excellence and enthusiasm that you expect of her. Don't put her on the defensive. Let's see what she really wants from going to college right now, taking time to ask about and to respect her priorities, goals, and concerns. Listen to her -- don't lecture or make this an inquisition. Put yourself in her shoes and remember who she is temperamentally. Freshman year is a new, often confusing time of life for kids.