Hi and welcome to the forum
The white dot on her butt is her ovipositor (egg laying tube). Sometimes the ovipositor sticks out a bit but it's not normally anything to worry about.
She might be in labour but she might not be. Make sure you have lots of plants in the tank for her to hide in when she gives birth. Don't move her. Do regular water changes and gravel cleaning to keep the tank clean. Make sure any new water is free of chlorine/ chloramine before it's added to the tank.