Hi, Peaches is a beutiful name for a fish. I named my swordtail alpha female Bun, I believe I had her for almost 3 years. I named her that cuz i am so creative XD
I have been keeping livebearers like 3 or almost years, but never had any success breeding platies. From experience I would say she is not pregnant or she just recently gave birth but as Fishorama said, give her couple to few weeks. She certainly will give birth as ususally livebearers are mixed in stores with males x females and female livebearers can store sperm up to a year, sometimes more. And given if you have an active male in the tank, they sill breed. If it not happens, they still will breed at some point. It took me a lot of time and patience to breed my swordtails together.
I will ask you few routine questions as I am put off by how pink/red their gills are and how unusually thin the bottom guppie is compared to your guppys and platys.
for how long has the tank be set up for?
Actual numbers for ammonia, nitrite and nitrate?
Size of the tank?
Number of fish?
Filter?
Is the tank cycled? For how long?
that is just me but i would go for a more natural look with some live plants, black (?) gravel or some sand and couple pieces of wood. Those are beauties! <3
given my Walstad tank, all natural (just ignore the filter lol)