"We both mock type as we speak."
I think it's something similar to what Carol said : pretending to be busy while being idle!!!
1. They pretend to type (work) when actually all they're doing is talking over microphone/ directly to the person
2. They actually type some junk stuff like "ndgjkjhdksjFKGkfHKgdfhgdkjfkj" so that ther others hear the sound of the keys being pressed and assume they're very busy
3. They both are on online chat, where they have facilities to speak even as they type :
SHE : Hi (then she says "Hi" over the mic)
SIS : Hi (sister also greets)
SHE : Whatcha doin? ( she asks something else like "Hows your hubby?"
etc. etc.
It's just a wild guess, bcoz that's what I do (mock type while chatting over some Messenger Software)