okay, your getting into some slang here.
but i will sometimes use it like i use dude, but referring to a female.
dude, i translate to be guy or possibly girl who seems to be pretty cool. and has similar qualities as yourself.
dudette, i would use for a female only. having the same meaning as dude.
i know its a bit confusing, being able to call a girl a dude or dudette, but thats the way it is. remeber this is slang though