In terms of hours, she certainly does 40 (or more) hours per week during the semester. She typically has to be at school from 8-2 or so, M-Th, but her actual schedule usually is more like M-F, 8-5.
So -- and intend no offense by saying this -- particularly assuming she's got some flexibility in when she actually works those 2 pm -5 pm hours on M-Th and her Friday hours, this is already a situation that many people would think of as "part-time" rather than "full-time." I in no way intend to suggest that she's not working really hard, or putting in the hours, or whatever else. But, from a parent's perspective, that's a pretty nice set up with lots of times to be with the kid even while working full time.
This is coming from a mom who's very, very happy to be in the workforce. The kind of happy that you'd have to pay me A LOT to get me to stay home. Now, sure, I like my job. But mostly, I like the fact that my key roles in life involve stuff outside my household and family (though interestingly on a recent mother's day "worksheet" they did at school my first-grader had to list "my mom's work," and his item was, "take care of me.").
A factor to consider not yet addressed in your posts is the availability of good-quality childcare in your area. We've got access to LOTS of great options (and can afford them), so putting DS in childcare/preschool/camps has never for us been a question of, "Oh, should we really subject him to this sub-standard situation." His paid care and schooling (and now public school) have been enriching, positive, and provided great opportunities to interact with other kids. But I know we are lucky to be in an area where that is true, and that not everyone is so situated.
Assorted other random thoughts: I'm an introvert, and time away from my (apparently) extroverted kid is essential. He wakes up at 7, goes to bed at 9, and talks non-stop between those two time periods: Aigh! Another issue: how much sleep will your kid require? Some need more, some less. Mine has always been toward the less end of the scale, meaning I never felt like I didn't have "enough time" with him after getting home from work or whatever. I mean, sure, there's a lumpiness aspect -- some days I have too many hours and some too few. But over all? Plenty. Last but not least, different people value time with kids at different ages differently, but personally, the baby/toddler/preschooler phase is far from my favorite. The older DS gets, the more interesting and fun I find spending time with him, and the happier I am not to have spent more time out of the workforce when he was little, thereby constraining my options for having time available with him today. Ooh, free bonus thought: add to that aging parents and the awareness that I may (again) need time out of the workforce at some point in the future to help them and I am
particularly glad to have been a working mom adding to my 'stash.