New Hen added and need some help!

I am a newbie to Urban chicken raising! In April I bought 2 RIR and 2 Silkie Bantams and have raised them together. They got along wonderfully and were all buddis!
Unfortunately one of the RIR's ended up a Rooster, which is not allowed in the city and I found a great home for him. Very sad, as he was the only that was tamest and loved to sit in my lap. In exchange for the Rooster, the farmer gave me a Hen that is a couple of months older than my 3 and was already laying eggs.
Naturally, the 3 girls were very skeptical of the "new girl", but after 3 days they seem to be getting used to each other. The new addition hangs back a little, but slowly getting closer to the others while they are in the yard.
So here is the ISSUE. New Hen, Etta, has stopped laying, most likely due to the stress of a new home. How long before she should start laying again?
Also, my RIR is right at 20 weeks, and when should she start laying? Will Etta laying help Aunt B to start laying??
Finally, how old are Silkie Bantams when they usually start laying?
I am in NC and temps have been in low 80's during the day, if that matters.
Thanks!!