I am thinking this might be the case here also as she has been growing pretty fast since i acquired her.Mine is about an inch and a half right now and she just started webbing yesterday,so i guess the next week or so will tell the story.My P. regalis always starts to web 1-2 weeks before molt and it does some heavy webbing with added substrate just as you described. Rest of the time, webbing is down, almost next to nothing. It has always done so, since it was about 1''.
I am curious if this is the case with yours?!
Regards!