i dont know how long till she will have them im worried her being in tank with other fish as need to get some floating plants as my last platy what had babys other day i only managed to save 3 the rest was eaten
Well, if you leave her in a breeder for several days and she gets stressed, you'll have more to worry about. Stressed moms may give birth early to premature babies, who rarely survive. She may also reabsorb the brood and never give birth, or could even die from the stress her body is under from raising the brood, and from being moved around and kept in a container. They don't like it. ^^;
Better to risk it and let her be with the other fish. You may not get many babies, or any for that matter, but mom will live to breed again and you'll have your plants later, yes?
If you have decorations in the tank, make small tunnels under them, put them near the glass too...sometimes babies will get under and behind them where adults can't reach. Under a big log I have in my 55 gallon, I dug under it and left a tiny space for the babies to get under, but not the adults. I often find them there.
As for plants, when you get them, I suggest thick chunks of java moss, and for floaters, I always suggest Raccia(crystalwort) since it can be thick, deep, and adults can't always get in there. Babies can also lay on top of it as well as in it. :3 It grows fast too, good stuff, but you have to corral it somehow or the filter will eat it.