Get her to email you and trace the IP address on the email. Search for IP Trace in Google and you will get a number of sites where you can do this for free. You can also run the pictures through Tineye or Google images as others have pointed out.
There are other no-no's in the email source, such as emailers sent from a mass mail tool, like the Bat or emails coming from an IP address starting with 10 (private range - hiding location). There are a number of posts on this site that walk you through this, but if you get stuck, I would be happy to give you more specific help.
Besides all this, if it seems to good to be true...
Almost forgot - as someone who chats a lot online, Nigeria or anywhere else in Africa is a bad idea. There is a reason why they can never access a webcam! Even if they do, make them do something online that proves they are reacting in real time and it is not a prerecorded video playing for you.