If she's messing the nests, eggs are imminent, like within days.
18-28 weeks is average onset of lay for most breeds, SG are derived from high production birds(I believe). She sure is pretty!
The voracious vocalizations are typical, and are related to egg laying but not like flipping a switch-'hear the sound and egg appears'. They will call out this 'song' before laying or after or when another bird is laying or not at all. I call it the Raucous Cacophony, I once had a group of pullets so constant and loud near onset of lay that I had to close the windows to my house to work on the phone.