If she hasn’t reacted badly to the bit with tongue over, she probably is not going to have a problem with wearing her bit this way. Does she steer as directed? Is she resistant to your rein signals with tongue over? Doesn’t sound excited about it, which is good. Might be looking for a rest stop while you fix things!
I have heard of that rubber port working with some animals, but not always helpful with that tongue over issue.
I have never had success with tight nosebands, raising the bit really high in the mouth. I am telling you he was grinning like a Movie Star, but still got his tongue over the bit!! Using tight nosebands of any sort, raised high bits, just prevent animals from getting tongue BACK under the mouthpiece to self-fix the problem, in our experiences with various animals.
We now leave bit fitted a little lower in the mouth, horse or donkey is NOT smiling when his bridle is on. Noseband is fitted correctly, you can get a couple fingers under when ready to drive. If horse gets tongue over, we just keep going. You can’t stop in a class, any competition, to fix the bridle anyway. So drive like you haven’t noticed a problem, horse or donkey gets no reward for tongue over bit, no stop, no rest. Often they will fix the problem themselves, if bit isn’t fitted up tight.
One of ours used to do that, had learned the trick got him a break with other drivers and owners! I fixed his tongue 5 times in a very short time span, not even getting back into vehicle as the groom, before he had his tongue over the bit again! Driver said " We are done fixing that problem, he can wear the bit like that and keep on working." So no more breaks or fixing, horse had his tongue back under when he got unharnessed in the barn! Every now and then he would “wave his tongue” at us to say it was over the bit, “Help Me!” But we never stopped to fix it again, so eventually he quit doing it. We did get asked “WHAT is he doing?” by spectators sometimes. We said he is waving at the audience!!
I would NOT use what are popularly called “Mule Bits” with the chain mouthpieces. Doesn’t matter what kind of chain, they are cruel and abusive bits, for strong-arming large, untrained animals in the past. You can easily cut the tongue, bars, with those terrible types of bits. Unless your donkey suddenly turned into some kind of idiot, there should not be a need for any bit like that.
Tongue tying is iffy, I have seen horses who lost their tongue due to lack of circulation with tie on too long, not done correctly. I wouldn’t do it to any of mine. It is in the “gadget” type of fix. When gadget is off, tongue is not fixed. As BLBSTBLS said, hers is on for VERY short time, not expecting it to train/fix horse not to get his tongue over, just to prevent the problem.
Donkey should be able to go on a bit like a horse, but will naturally be slower moving most of the time. She should be light, responsive, accepting of the bit, when trained correctly. Donkeys are NOT stupid or insensitive, though too many people treat them that way. They are just slower decision makers, need to trust you, to be your good driving animals. Just a whole different mind than horses.
You have to be sure to get a wide enough bit, even for short donkey, since their skulls are not “refined”. Could even need a 6" bit, to make her comfortable in fit for not pinching her teeth against skin. Measure her mouth to learn her correct size, before purchasing a bit for her. Farrier might be able to flare out the reach part, where bridle buckles in, to prevent pinching above the mouthpiece. We did that flared out on bit for some Fjord horses, very wide at the molar area.
I always get some kind of a port in a curb bit, arch, mullen, low or regular port, for tongue relief when reins are used. Fat tongue, low upper palate, can make mouth crowded with a jointed bit poking upward or straight bar pinching down on the tongue as reins are used.
Idea 1: is to get some bit latex, wrap where bit lays on her bars for cushion. A narrow wrap or two on mouthpiece for if she persists in putting her tongue over mouthpiece. At least her bars are then protected some, not metal on bone, while driving. They do spit a lot when latex is new on the bit. Everyone will think she is “using the bit well” seeing the spit! Ha Ha
Idea 2: is dried fruit leathers, wrapped on the mouthpiece then squeezed tight so it sticks on, for her to enjoy after being bridled. She might like rubbing the fruit with her tongue, help keep tongue under to enjoy the flavor better. Fruit lasts about 15 minutes before swallowed or licked off, but might be helpful to keep tongue under. She might drool in color too! Ours like Strawberry best, but like all flavors. Fruit Rollups, Fruit by the Foot, are both sold in stores and work well for this.
Keep us posted on your progress with her.
She has a 5 mph walk- steady, forward and eager. Think of a lady in a big shopping mall. She has just walked into a department store at one end and glances in her purse and sees that she left her wallet on the counter of the other big department store, clear at the other end of the mall. She turns and walks with purpose and authority back to the store. That is how my donkey walks. She also trots lovely!!