My email is being intercepted

For a couple of years, people have told me that a former employee was using my picture and name on her work email account through reagan.com. Both she and I tried everything I could to remove my name and picture from being associated with her account, but we never found where my info was being pulled from. She said she would close the account, but never did, and then moved away and I lost track of her.

Yesterday, I was forwarded an email from her to a mutual friend. My former employee had replied to an email that was sent to me - and only me. When I checked the address path, sure enough, my Mac mail was the only addressee. But she definitely received it and replied to it, not noticing that it wasn't addressed to her in the first place!

On top of all that, in the last month, I have been battling online identity theft and fraudulent transactions (such as opening new lines of credit in MY name!) that are centered in the area she is said to be re-located to! It might all be related, so I need to do some research. Is there a way to find out if she has been intercepting my emails all along? She would get all my online banking statements, my credit monitoring reports, etc. How do I determine if my emails have been compromised?