Are you planning to try and save the fry? If so, a breeder net or lots of plants-especially floating at the top (live or plastic)-would help. Livebearers tend to eat their fry.
Ok. I've never had a plastic one but I'm sure it works like a net one. As for fry food, you can always put some flakes in a bag and use a rolling pin or whatever to crush it up. Fry don't need much-just a very small pinch a few times a day.
Oh. I was thinking more of letting her drop and then putting the fry in there till they were big. Breeder boxes and nets can cause dead babies and stuff. But some don't mind it. Some of my fish in the past I let birth in the tank, others I could move to the net to birth without problems. just depends on the fish. So yes, if you more her to the box, make sure she has "squared" off. Plus around that time they get shy and can act different than normal. You'll get to know what to look for. Plus, if she does have problems, then you know what not to do. (They have fry monthly anyways, so I wouldn't worry too much.)