Where privacy and IF collide...

This is tricky for me. It seems that the post 9/11 world has made privacy the new "black", if you will, especially now that we have FBI director Mueller testifying about thousands of phone numbers obtained through sketchy methods by his agents. I sort of ran into the same situation this week...
While working at the reference desk, I was approached by two women. One of them asked me if I had heard about the missing teenage girl who had supposedly ran away a few days ago (it was in the news apparently). I told her that I had not.
She then explained to me that she was the girl's stepmother and she wanted me to look into our "system" and she if she had been in the library to use the computer or check anything out. The pit in my stomach reached up and started to choke me right in front of them.
I got it together and told them how sorry I was and that this must be a difficult time for them and then went into a very surface level discussion of patron confidentiality based on the RCW and that I could not help them with their request. As you can imagine, the emotional tone of the conversation began to elevate. She then asked for the building manager, who happened to be me at that moment because it was the last hour that we were open and there were only two other part-time librarians and about 12 circ staff members in the building.
So we talked it out - I tried to talk it out anyway. Patron confidentiality is a very very serious issue in our library system, as with most other systems. While there was no way that I was going to do what she was asking me to do - you can imagine the internal conflict that was brewing inside of me as I placed myself in her position. I tried to find any wiggle room possible - asking her if she signed the application as the guardian (since the girl was under 17 when she got her card - per our system's policy). She had not.
Then she told me I was a murderer and would rather see a dead child than cough up a list of her daughter's library activity...