I can really relate to that. I mentioned a few times I had big issues with silence in general between two people [on account of my parents] all she would do it sit their no moving a muscle or uttering a word. I would up ending the session 20 minuets early once.
Some times I feel so annoyed with her I think she is staying silent for her own benefit. ie if she stays silent she cant get herself in to trouble or something like that. Paranoia on my part I guess.