treat her real nice, (you probably already do) boil up some confidence, and at the right time look her straight in the eyes and ask her out... you should get an honest response...

rejection isnt so bad, lol i remember i asked some girl i really liked to go out with me on valentines day (thinking she liked me too) and she said no.. but i was glad i asked and afterwards she did become more friendly towards me... lol it took some balls too...

good luck man... its all on you...