You can develop your own configuration file and script to send to a friend for the purpose of receiving her IP address in return, but the process may be overly technical for some. Alternatively, you can visit a site already equipped with a working script that gives you a link you can send to your friend. Once your friend opens the email and clicks on the link, you will be emailed that friend's IP address, but you may be leery of trusting an unverified third party with such information. If you want a simpler and safer way to locate your friend's IP address, you can view the source information of an email that your friend has sent you from her own computer.
Using an Email Header to Locate an IP Address
View your email inbox and locate an entry from the friend. In AOL or Outlook.com, right-click the email subject and select "View Message Source." In Yahoo, right-click the subject line and select "View Full Header." In Gmail, click to view the email, click the "More" icon and select "Show Original." Hold down the "Control" key and press "F" before typing into the pop-up field "X-Originating-IP" or "Received: from." The IP address that follows is for the computer that was used to send the email. If there are multiple "Received: from" lines, the last entry typically contains the sender's IP address.