Molly breeding

While she's pregnant, no you don't need to separate her from the rest. When she drops the fry, and if you want to ensure the fry will survive, then yes it's best to move her to a separate tank. In fact, you'll need to move her back to the main tank when she's done dropping the fry, because she'll turn around and eat them as well. When she's getting ready to have them, a hormone will kick in, and she won't eat regular food, nor will she eat the fry during that time. But once that hormone is done working, she'll be ready to eat them. The gestation period for livebearers is about 28 days, give or take a few days either way. You'll know she's getting ready to drop the fry when it's close to that time, and she'll start hanging at the bottom trying to hide from the other fish. Usually the males will start to pester her then, to cause her to drop them so they can eat them.

I had molly fish in the past. I think you should separate the female one because she is pregnant now. It is easy for other female molly fish eat the babies rather than the male ones. I love China