Caesarean section, also known as C-section, or caesarean delivery, is the use of surgery to deliver babies. A caesarean section is often necessary when a vaginal delivery would put the baby or mother at risk. This may include obstructed labor, twin pregnancy, high blood pressure in the mother, breech birth, or problems with the placenta or umbilical cord.
Being sterilized or using any other means of contraception don't have anything to do with observing Iddah period.
In fact preventing Ikhtilate Miah* is one of the reasons of putting this law and not the entire reason.
It is said that the respect of the previous marriage is among the reasons.
Unless she has reached the age of menopause, so in this case there is no need for observing Iddah period.
*It means the mixture of semens and to avoid uncertainty in whose child the foetus will be, is intended by it.