I don't see a problem with that. His place has to be paid for regardless if he goes, or he would loose it. Why waste money, the days are paid for, she might as well use them.
But on that note, she may have plans to keep him home a day or two each week, depending on what other things she has to do in those 6weeks. She might just not have any firm plans yet. A teachers job doesn't end when school does unfortunately, they have a lot of prep work to do at home.
Try not to read to much into it and jump straight to PND or selfish etc. She's still probably finding the balance between work, her baby and time for herself. Her son would have a familiar routine with going to nursery during the week and it could completely disrupt his moods/sleep to change it up too much just because schools out.