Malicious email

Trying for advice on this email I got demanding $1900 in a day ; started with "I know your password " and quoted it !  I only use that for AVG . IolantheStromberg ,(by bad memory, I blocked it) @outlook.com   How did she get that ? 

Hi Terry,

We will certainly help with your concern.

To check it further, I have sent an email requesting more information.

Please keep up the conversation via email for further assistance.