It's been awhile since I saw a birth of my livebearers, but if I recall correctly, mine used to hide at the top or bottom of the tank, towards the back.
Depending on what color your molly is, when she gets closer to delivering you will see the gravid spot get closer to her opening. The black dot will look bigger on one side then the other. That's just from my personal experience.
If you plan on putting her in the breeder net, I would do it at least a couple days before she delivers, so you can give her some time to adjust to the net.
The stress of the move, and the stress of being confined could result in a premature delivery (still birth). And unfortunately, I've also experienced that too.