Nice fish. Dalmatian Mollies, aren't they? I keep "Livebearers" too. These fish feel most comfortable in heavily planted thanks. The fry will immediately go to the surface for a quick breath and need some floating plants, like Brazilian waterweed (Anacharis).
The female will hold off giving birth until conditions are just right. I'd keep the water as pure as possible with large, weekly water changes and make the new water a bit warmer. If the female is close to giving birth, a lot of pure, warm water will help.
One other thing, if you're not using a bit of standard aquarium salt, you really need to. I add a teaspoon to every 5 gallons of new water. This is important, especially for fish that give birth to live young. The properties in the salt will strengthen the fishes' immune system. I've used it for years with good results.
"Fear not, my young apprentice. Just change the tank water."