Tiger Barbs are egg layers, not live bearers.
She's likely just got a load of eggs ready to drop.
There are lots of articles on line on breeding Barbs, they're one of the easiest egg layers to breed.
You've got a good start with setting up a breeding tank.
Did you notice if she has paired off with a particular male?
You'll need to put him in the tank with her while you prepare the breeding time table.
Do you research and good luck.