Office Dullard

So I work at an office where the front door is locked all the time. I have a button under my desk to press which opens the door if I see someone coming. If I don't see them coming then I open it when I see or hear them pushing on the door. This is usually what happens with the mail man, the Fed Ex guy etc. Everyone who works here knocks if I don't see them, but there is one person who works here, she's been here longer than I have and she never knocks on the door if she sees that I'm not looking, she just pushes and pushes at it. I wasn't sure what to make of it, until today when I was in the area of the front door but not anywhere near my desk and I saw her pushing and pushing on the door. I walked over to my desk and pushed the button thinking that perhaps she didn't realise that the door is locked. So when she came in, I pointed out to her that I had to unlock the door with a button before she could use it. She said, "I know, I hate that door."

What do you guys think the motivation behind this futile door pushing is? It's so odd, I know it's a little thing, but little things about other people are always so much more noticeable at work.

Do you think the next time she comes to the door and I'm not right at my desk I should just let her push it until she realises that if she wants to get my attention she has to learn to knock like normal people?