I agree you should reschool her.

I'd put her in a mullen mouth bit and teach her to be ridden, and to carry herself with no contact at all.

Riding her in a contact, as you would be inclined to do, will give her something to seek to lean on. If you ride her without a contact, what does she have to lean on? Also, if you have a contact, you would be inclined to give the rein, then retake it, if she leans, when actually, if you teach her to go forward without a contact, thefirst time you take up the rein, if she tries to lean then, you can take the rein until she softens, then give it and she should go on as before.

Giving the rein when she leans will only encourage her to lean when you take it up again.

Throwing away the contact until she learns to carry herself, then taking up the rein when it is needed, rather than having constant contact, and stopping any attempt to lean with  solid hands until she softens, then giving at the instant she softens, is the correct way to discourage leaning on the bit.

Try it. 

 what the others said but also, whatever bit you get... it has to be comfortable for her, because there is nothing worse for a horse than a pinchy bit! :( if your bit is to tight or pinchy, it can seriously damage your horses mouth with will A)hurt it AND B) it will toughen her mouth which makes her harder to steer in the future! 

goodluck,  i hope you will make the right desision! :) im sure you will be fine! sorry my advice didnt help much, the other comments covered it all! i just wanted to slip that in! ;) xxxx