Try a fumler (full cheek) bit and lots of turning exercises like circles, serpentines, figurers of 8 etc.
Also try long reining or riding though poles shaped in a S like shape and weaving though cones.
Not sure what steering issue you are having but it is not unusual for young horses to be rather wobbly and also slow to turn.
I always start my youngsters with a bit with full cheeks so that the bit doesn't get pulled through their mouth. It also has the benefit of giving them a bit of a clue as to what you are asking them to do.
Exagerate your aids. Open your hand wide in the direction you wish her to turn. Plenty of inside leg support and your weight in the direction you wish to turn.
Young horses need time to learn what the aids mean (it might help to have someone on the ground to help you both) and some seem to take a long time to react.
The important thing with young horses is to ALWAYS get the right reaction and to praise them when you get it. Repeat and repeat again.
I put mine in a fulmer to begin with and had to make sure my aids were really clear and well enough in advance. If you didn't ask my boy to turn he would just run into the fence which was fun!
She was in a sweet iron full cheek snaffle, now she is in a apple flavour happy mouth full cheek with a roller in the middle snaffle. This is also a bit thicker than the sweet iron.
Use a full cheek bit and make sure you open your rein to lead them when turning, at this stage do loads of work in walk and a really essential thing is for you to look where you want to go...
It may be you need to go back a step to long reining, we ensure we can steer perfectly before getting on board, including turns and halts, so if you have not spent enough time doing that always go back before going forward if you get my meaning.
Longrein longrein and more longrein. When first starting get a friend to lead or walk by the side, then when you feel confident the horse is listening to you, take the leader away.
It does take a while for some horses to get used to steering! Use lots of exaggerated aids, open out your hand when asking for a turn, and lots of inside leg. Make sure you do lots of turns, circles, serpentines etc.
Also, make sure you are firm, don't just let her wander in whatever direction she chooses. Let her know that when you say go this way, you mean it not 'well only go this way if you really want to'. A nice active walk will help to achieve this. Make a point of planning when you are going to do turns, and prepare well in advance, so the horse is ready for it.
I've found with my boy (newly broken too, but I broke him myself so no idea if he's the norm ) that you need to steer much more with the seat and legs than with an older horse, or it confuses his little head!
I would recommend a lottt of groundwork, also try having someone leading her while you ride, does wonders If you give the aids for turning and they lead her the way she should be going, usually helps it to click!