leave her a note or ask her in person (ladies ur opinion) please ?

im just trying something new never asked a girl whos older than me out.. shes 30 and im 25.. we both are intern at this one hospital, shes in a 6 months program.. im just and observer and i had the pleasure of working with her for the past two days. shes friendly and playfull i noticed she called me a dork and kinda flirted with me .. i would like to get her number and eventually ask her out. unfortunately due to the busy enviroment in the hospital i dont get to talk or see her that much... tomorrow is my last day at this hospital and i probably wont see her ever again if i come back some months later... so should i leave her a funny note and write my number..... or should i ask her out directly ???