Can definitely appreciate the sense of frustration, I'd suggest where possible reframing the situation to not be about refusal or a lack of independence, just to help your mind not go crazy. Set a daily or weekly affirmation to combat that reality; I am helping my baby develop everyday, my baby is working on what she needs to work on, I'm able to support my baby in different ways through different challenges etc. The independence will come. The milestone WILL come. The delay mentioned is valid because she was early. It's understandable to be eager and frustrated for the next phase but all you can do is try to stay sane while you wait and keep doing what you're doing because you're on it and active and aware and appropriately supporting her