I woud think that just saying her name before and after the whistle (and always remembering to do this consistantly and praise her a whole lot when she does it right!) would help her to assocaite the name with "come here". After doing this for a while (Weeks, maybe months. Until she does it every time, or nearly every time) you could start taking the whistle out every once and a while until she eventually doesn't need it at all. Since she's so young though you should always remember to keep any sessions with her short and to the point, with lot and lots of praise.