I would say with a 3 year old avoid using strong bits and fixing the base problems. Otherwise she'll end up with an unsensitive mouth and youll have to keep upping the strength of the bit 😊
If you want to be really crazy: hackamore hackabit and kineton nose bands are also work. Kinetons make for VERY good brakes
A Waterford could work well but I'd also suggest you work a lot on getting her to soften up and respond to your aids. She's young so you've got plenty of time to get all kinks out 🙂. Also if she doesn't like the Waterford other great option are happy mouth with a roller link or copper roller bit. She won't be able to hold onto the bit or lean into it since it'll just roll. It'll also give her something to do with her mouth and they're both fairly gentle. My horse used to use a happy mouth roller link. The copper bit also encourages a soft mouth.
Thank you for your answered and @mayatrevorrow
I find your advice useful I will try it :) x
It would be a good idea if she reacts well to gentler, bits but if she needs a stronger bit it might not be such a good idea. Also if you have ridden her in stronger bits and she is fussy in them then she might react better to a gentler bit. It would probably be worth a shot.
I find that the bit shouldn't really matter as much because the bit shouldn't be what controls the horse it should be you that does. I suggest finding other ways to slow the horse and control her more. I have a very forward moving horse and we have always had the same bit. He used to pull alot but if you do lots of work with them they tend to give up and listen to you. Lots of ground work and lunging may help a bit to tire out your horse before work. When riding also you lots of half halts and releases and give her the choice to listen to you. Sorry if this wasn't quite what you wanted but I hope it helps a bit with the problem 😊