I really don't know...maybe she's just truly too lazy? LOL Maybe she'd flick it more if you handle her more...as in "more stimulation"- more reason to sniff new things?
If you've seen her actually flick her tongue in a normal manner, then it shouldn't be anything neurological, but if it never comes out all the way, maybe there's a slight
impairment...maybe a muscle weakness (that controls the tongue)? Dunno, just guessing...