The easiest thing to do would be to create another file system watcher similar to the one that you already have watching for the FTP file and then when the file appears simply send the user and email that the file is there and remove the email part from the procedure.

A bad thing to do but would work is simply in the procedure that sends the email do a loop that checks for if the file exists and if it doesn't sleep the thread for sometime and then check again. If it finds the file then email the user and exit the infinite loop.