Another way to know when she is almost ready is if she starts hanging around the heater. Then it should only be 2-3 days. That's how I know when mine is ready. Unfortunately, I was waiting until she stopped eatting (another method to know: some livebearers stop eatting a day before delivering), this is how I used to know when my guppies were ready. Needless to say, it didn't work on my molly today and she had them in the tank last night. I caught roughly 35 which is a good number. I'd light to have seen how many I would have gotten if I would've put her in a breeder box. Good luck!