If your female molly has been in the presence of a male molly in the last 6 to 8 months, then she is most likely pregnant. Livebearers, once fertilized, usually have fry every 28-30 days. Livebearers can also store sperm for a little over 6 months. No special care is needed. If she does produce fry, some floating plants would be beneficial to provide cover so the fry are not eaten. Here is a read on the matter: http://www.tropicalfishkeeping.com/member-submitted-articles/livebearers-unusual-breeder-83402/