Maybe she is all of the above things, but maybe she is also an experienced mum, who has given birth 3 times over, relatively easily and felt that she could manage going back to work.
Sounds to me like it wasn't physical activity and she probably had a few meetings and drank tea. Does the fact that she sat in a few meetings mean she was paying any less attention to her baby or meeting her needs? - I found it tough to meet my second LO's needs with a toddler in tow, right after the birth! - hope that doesn't make me selfish .
Personally, it isn't something I would want to do. But I do think good for her to give the girls she teaches a good view of "motherhood" in all of its glory, something, sadly, that most girls/women don't ever see these days and as pointed out, help remove stigma relating to childbirth, as if it is a disease and breastfeeding. And if it can help stem the rising tide of teenage pregnancies that that is a positive thing.
To play devils advocate, how is going into "work" different from having to look after her other two kids, house etc right after the birth? - Frankly, having to do that is harder (IMO). No one gives us two weeks off from that work (and no, paternity leave still doesn't alleviate that issue - in my experience )
Many women around the world have to go back to work, or give birth whilst working and then go back to it. Sadly, they have no choice in the matter. I wouldn't call them selfish.
I think this is a relatively unique situation. You certainly wouldn't find me going back to work. I am dreading having to go back after 6 months and if anything I am more knackered now than I was immediately after the birth.