The school should be reporting to DOCS if there are large numbers of absences. Legally kids must attend school (or be homeschooled) and large number of absenses are often a sign that there is more wrong here.

I think you should tread carefully and if you do choose to become involved I agree with Zarava- I'd do it from a place of asking if she needs help. Mums can be quite overwhelmed at times. Maybe there is more to this than her being a "lazy" parent. Maybe she needs help, even just someone to talk to?