Can I blame Hotmail?

I sent a friend an e-mail and it turns out it wasn't her e-mail, but rather a friend that she hardly sees anymore. I had attached her name to the wrong e-mail. I know that when I selected her name, I felt some confusion. Several months ago, Hotmail updated their UI (User Interface, what you see on screen/how you navigate) and I hated it. It put almost all my e-mail contacts in my shortcut list, so I was searching the 50+ list for her name. I found one I thought was hers and used it. Obviously that was a mistake! How embarrassing for me! And maybe for my friend since the e-mail involved money. Big opps! At least she laughed about it.