guppy? do you mean molly? Sometimes they can hold longer....closer to 28-30 days. I do have a couple guppy tanks and I just let them release into the tank...we have live plants that the babies hide in.
We do still have our aquariums...down to 6 though. I'll try to take some new pics soon while the floors are clean!
I'm not sure about mollies. Guppies get a gravid spot that gets darker as the babies get bigger. I would think the only way to make sure you get the drop (babies) is to isolate her in a separate tank. Of course she could have dropped and eaten them!