Maternity leave extension?

So I'm coming up on my final week of maternity leave 😣 my mom has been trying to get me to take more time off since the beginning. before he was born i decided to take 9 weeks off, even though fmla let's you take up to 12, I'm a teacher and just transferred to a new school. i figured i would just miss the 1st quarter and be back for the 2nd. I was sent to be induced the first day of school, i had pre-eclampsia and became toxemic, a very rough labor/delivery that ended in a c section. i stayed in labor and delivery unit for 4 days. I'm feeling much better, blood pressure had improved, but I'm still not 100% I'm worried about asking to extend my maternity leave. Is it unprofessional to ask for more time? I know they can't deny me the time, but I'm worried about upsetting the new principal before I've had a chance to really work with her. Any advice?