As much as you need to pay attention to having her give to the bit, you also need to pay attention to never holding onto the reins when she has given. I mean, never pick up the rein unless you are asking for something to happen, do not release until it does, and never "ride the brakes". So, never have the reins in a static hold while the pony resists in an equally static hold.
It's ALWAYs , pick up rein, ask (and have your seat be saying the same thing), GET a change, reward and release. Always ask with the kind of softness you want her to arrive at after her training. Get as firm as is necessary, but always start soft.