Managing personal Outlook.com account settings, security, and privacy
Sorry, when I said I'd changed my email address multiple times I meant I'd changed my password multiple times. It doesn't make any difference. I still constantly get these emails, and she was somehow able to use my email address to sign up for Facebook and Twitter (meaning she had to confirm these subscriptions via email). And my recent activity includes mostly incorrect password events, dozens of them, most of them not involving me. (they are all listed as US)
Please read the post by jFiredog for an explanation of how this can happen.
If your email address is associated with a Facebook or Twitter account, then maybe you can request a password reset for those account and lock them!