These kind of things are strange because I have a Mustang gelding whose tongue was almost cut off by the first owner's bit. I am his third owner and I didn't even know he even had a tongue scar until I had owned him several months and just happened to see it. He takes a bit just fine, even though it looks like the bit rests in the scar. And when I say "in" the scar, I mean IN the scar. It's a horrible looking, miss-aligned rift in his tongue.
So I could totally understand if he had trouble with a bit but he doesn't for some reason.
If the bit isn't actually causing her pain and you just want to try something flavored to get her to accept it, try wrapping a fruit roll-up around the bit.
That's what I do with my 2 year old to get him to take the bit willingly. He loves it!
If that doesn't work after a few sessions it might be that she will never be comfortable in a bit due to her physical tongue problem. No one can blame her for that, it might be very uncomfortable. I guess it's a matter of figuring out if it is a mental issue or a physical one.