my blue spotted platy

Yes, a separate tank would be a good idea if you don't want them to be a crunchy part of the circle of life

Do you have one ready?

If she gives birth tonight the breeder trap could do the trick, but you'd have to put the fry somewhere after that...

I'd recommend you place her into a separate aquarium to give birth and just stock it heavily with fake plants/hideouts for the fry.

Those breeder traps have never worked for me because the mother gets so stressed out that she aborts her brood (in my experience, others have more luck)

Also, if you do decide to move her to a separate aquarium, make sure that water conditions are fairly close to those of the main aquarium to minimize stress.

just my two cents

I hope you're not considering moving her into the cycling tank. I would never use a breeder trap either.
I would leave her alone. If there are hiding places for her and the fry, it's much better to leave her alone than to take her out when she's so pregnant. And in any case, platies can have lots and lots of fry at once, it's not like you will want to keep all of them. The way I look at it, the fry that survive in the main tank are the strong ones - natural selection on a small scale. I get a little sad too when a bunch of fry are born, and then I see them slowly disappear - but do I really want each of my females having 10-20 fry once a month and keeping all of them? Usually one to 3 fry survive from each batch, and even that is plenty for me.