My suggestion (if you can get past the bit grabbing) would be to lunge her in the bit with side reins if you know how. Let her have it in her mouth for a bit before you ride. Are these the only 3 bits that you have access to right now?
I imagine that if you go straight from the kimberwicke that has some curb action and a chain, right to a loose ring snaffle your probably going to feel as if you have no breaks at all. So if you do go straight to the loose ring I would suggest starting super slow, maybe lunge her with her bridle on 1 day, next day ride her in it but only at the walk(lots of transitions, circles) ect ect ect
Im personally a fan of the slow twist dee rings. It worked wonders for me to get my pony onto a rubber bit. But in the end its all about what you and your horse are comfortable with.