Right under where you put your subject, it says attach files. Click on that and it should give you a list that says "File 1" then blank, then a "browse" button, then "File 2" then a blank, then "browse" button.
What browser are you using?
Another thing is this...you can post them in York (do you have a york account?) and then "share" them with her and she can make a york account and access them that way.