Sounds like she's been in the tank with males, so she is pregnant.
What we did with our pregnant platy was: gave her lots of plants (fake) in the tank, including a bunch of them planted in a corner of the tank away from the filter. We also wrapped fish net netting around the intake tube of the filter and changed the substrate to flat glass marbles (for the fry to hide in). You could also put some caves in and some floating 'guppy grass'.
Any or all, the goal is to give the fry places to hide until you can fish them out. Taking the fry out is a bit of work, but you'll get the maximum to safety by first taking out the adult fish (into a large covered container - you could put the airstone in with them too if you want). Then carefully take the decor and substrate out (into another large container with enough tank water to keep it all wet). A turkey baster is how we'd catch the fry and move them to a container with some tank water in it. They hide VERY well and you'll even find them in the debris on the tank bottom. I'd go ahead and clean the bottom with the turkey baster, being sure to not throw out any fry.
Once they're out of the tank, you can
acclimate them to a tank for raising them in. Ideally a 10g or more with either a sponge filter or a filter setup with the fish net netting over the intake tube. Leave the bottom bare for easier cleanup and put some caves and maybe plants in for them to have places to feel safe in and swim to when they want to hide.
For food, we crushed a combination of foods into powder and fed them 3 or 4 times a day the first month.. moving to crumbled flakes as soon as they were able to eat them. Cyclo-peeze flakes and Omega One veggie flakes are what we'd recommend.