None of my gups ever showed any signs before giving birth, mine still eat swim with the others, acts normal. The way I can tell she is ready anyday, is her stomach will be very large around her neck, then u will see where she is getting bigger near the anal fin, like the fry is moving toward the back, and he poop hole will look swollen a bit...when I see that my guppys looks like that have a square stomach from behind then know it 24 hours max before birth.