Sometimes right clicking on an image and selecting 'search google for this image' will bring up a google search window and sometimes it'll let you know who the person/model in the picture is. I'm not sure if right-clicking works in non-google browsers, however.
The best I could find when I searched using your avvie was that she might be a girl named Serena but I couldn't find any other images or a full name for her. If you are looking to find someone with more pictures/more famous you can send me a PM and I might be able help!
As for returning, if you are having Mavis return next term as a third year, keep an eye on the Gryffindor OOC forum. Before term ends there will be a returning character thread posted there and all you have to do is post in it to let Aubrey know Mavis will be back! And if you're earning levels keep an eye on the Room of Records forum over on the castle board. Grades will be posted on the 21st and then you can start a thread claiming the levels you've earned this term!
Hope this helps, let me know if you have any other questions!
