sep.11th. "Who is she?"

'Who is she?'
I was trying to remember her for more than 40 minutes but I couldn't.
Today, I went to Riverdale elementry school for attend band student parents meeting.
When I arrived there, music teacher announced something."Thank you for your attending, give your child to courage, don't forget exercise, we need your help..."
I was trying to concentrate on her words but I felt boring not longer.
So I looked around right and left. At that time, I saw her who smiling to me.
I showed smiling too but, I couldn't remember who is she.
'She looks familiar and I have seen her somewhere.'
While music teacher's announceing are countinued, my mind went to the top of my head for find her.
I saw several times with a sidelong glance but I couldn't find any clue.
All of them are finished and I went to the parking area to met my husband and children.
They were waiting me for pick up.
When I opened the car door, he said, " Why you didn't say hello to her.""whom?"
" Eddie's teacher."" where is she? ..... oops."she is my son's teacher.
I went to her and said very carefully, "I'm so sorry. I didn't recognise you. I saw you in band class and I thought that you are not strange. I was trying to remember but...."
She just smiling. We said more about my son but I couldn't hear her.
I was very ashamed because we met just 2 days ago.