She looks VERY pregnant!
Do you have any fine, grass-like plants in the tank? If not, you can pick some fake stuff up meant specifically for the babies to hide in. Otherwise, your Mollies will have a feast when she gives birth.
Here's a link for the product to look for (or something similar):
[ame=http://www.amazon.com/Penn-Plax-Aqua-Plant-Hide-Out/dp/B0002565KM]Amazon.com: Penn Plax Aqua Plant Baby Hide-Out: Pet Supplies[/ame]
Afterward, put the babies in a breeding net/box inside the aquarium. They'll need specific food, too. You can ask about that at the fish shop, since it escapes me right now.