It can be kind of hard to tell with Balloon Mollies, because they always look pregnant! Usually you have to go by their attitude, and sometimes they WILL look a lot fatter though. Signs she is about to give birth usually include chasing other fish away, hiding, and generally acting moody.
If the little fry is Pinkish orange, I'd say it's a Platy. Yes, they do kind of look alike at this point..But if you have a sunset Platy, I can almost guarantee the baby came from her.
If you want some of these fry to survive, you can try putting in a few floating plants. Babies can usually hide in there. Or alternately, you can get a fry tank, which will probably be best if you want to raise these babies, as your tank is kind of small.
Of course, then you get into the problem of raising the babies in an uncycled tank, which can be bad for them, because they are sensitive. Maybe ask your fish store if they could give you a small piece of sponge or something, that's already been in one of their cycled tanks?
If you do want to get a fry tank, you could probably get by with about 10-15 gallons. If you want to raise them in a seperate tank, you'll have to net them out of the tank once they are born, or put the mother in there right before she is about to give birth.
Fry foods are good for the first few weeks, along with Baby Brine Shrimp. For fry foods, I recommend are Tetramin Fry, and Hikari First Bites. You shouldn't just feed Baby Brine Shrimp, because it's very high protein, and that can cause some problems like bloating...Best to intermingle it. After they are big enough, you can move on to crushed flakes foods, and also keep using the Baby Brine Shrimp. Ideally, You can alternate the Brine Shrimp with freeze-dried or frozen foods like Bloodworms, Daphnia, Tubifex Worms. Variety is good. Mollies also like veggies, so you can blanch a very small piece of Zucchini, Cucumber, Lettuce etc.
If you are going to have a fry tank, I recommend a sponge filter, so the fry do not get sucked up. You'll also have to do water changes pretty often, because fry need good water quality. You can do water changes using an airline tubing siphon, or a turkey baster.
Best of luck!