I use my jr. cowhorse with the roller for most everything I do. It is a wonderful, versatile bit. Enough bit to get your point across should you get into trouble but at the same time so wonderfully light and soft for the horse's mouth.
However, bear in mind this bit is only going to be legal in speed events such as gaming, team penning, etc. You cannot show in other events with it. Maybe jumping you can, but I'm not sure what the rules for that are. That's not my sport, just know I've seen some interesting bits on jumpers just like on barrel horses (Which is my area).
I would look into a thinner snaffle if I were you. Or, a hackamore like a Little S hack since she is responding well bitless. If you do go to a bit however, whatever you choose, may it be double (Or more) jointed and not single jointed. Would help it mold, as the above poster mentioned.
You could maybe even try something like a chain snaffle, though that's not legal in some things either. That one I know you can jump and do cross country in, but no dressage, western pleasure, reining, etc. Same deal as the Jr. Cowhorse. Speed events only.
Finding something to show in would be hard, especially since you aren't sure if you're going to be at an event requiring a bit yet...For now, I'd just look into the Little S Hack.
Pssh.I didn't pick up the wrong lead
It's called a counter canter...
...A very advanced maneuver.