Sometimes, a woman is given restrictions during her pregnancy (i.e., activities that her job entails that she cannot do while she is pregnant) or she is told by her doctor to stop working at a certain point in her pregnancy for health reasons. If either of these happen, you must abide by whatever the doctor says.
Regarding restrictions, you need to understand what she can do and what she cannot do and provide her with work within her restrictions, if you can. If you cannot--as some small businesses cannot--send her home until she either is given restrictions you can accommodate or her doctor removes the restrictions.
Normally, a woman who has a baby has a checkup about six weeks after giving birth. At that time, her doctor usually provides her with a release saying that she can return to work. Sometimes it takes longer for the woman to recover (e.g., cesarean birth). She should let you know about her projected return to work date as soon as she knows it.
While many employers do carry disability coverage or offer it to their employees at employee-expense, you are not required to carry or offer disability insurance for your employees.
If you do and if she enrolled in the plan, she can collect disability payments while she is required to be off work by her doctor. You are not required to pay her any salary while she is out due to pregnancy/giving birth except for whatever your employee manual specifies for accrued vacation/sick leave. Most women save up all the paid time off work they can to use when they leave work to have their babies.
Your company is too small to be covered by the Family Medical and Leave Act; so technically, you do not have to give her more time off work than the doctor says she needs for health reasons. And if you must, you can replace her, as well.
If you offer medical insurance coverage, be sure that she knows her responsibility to pay the premiums for her coverage and how and when to do this before she goes out on her leave. Many employers do pay their usual portion of the premium for the employee while she is having her baby--but it is not required.