I wouldn't assume she is dumb just because she has no reply.
Girls can have intelligent conversations, a lot can be related whether they are passionate about the subject. Girls have a right to have no opinion as do many people. Maybe her thoughts were focused elsewhere or she didn't want to have a serious conversation at the time.
Another thing.. What if the WTC didn't impact her the way it did you and she really had nothing to say about it. I know if you asked me that questions I'd say it was just another act of terrorism.
I think it is you that are torturing yourself. She has no response and you interpret that as torture on yourself. let me stretch that a bit and give an example:
"So how about the lakers this season Sally?"
"I dunno" --
"DAM, WHY MUST you torture me so much -- STOP the mind games! I'm leaving you"
hehe
