She says you cannot make just your hands quieter. Well even if you are loosey goosey, your hands will still be a mess if you aren't aware of what they're doing. Every part of you can be isolated. Fingers, toes, heel, calves, hips, thighs, neck, head, eyes, abs/core, small of back, upper spine, lower spine, seat bones/pelvis, inner thighs.. do you need me to continue?
Yes they all work together, but even if you are the best quiet BODY rider in the world, that does not ensure that your hands are quiet as well. You need to make the effort to build muscle memory, to remember to release your elbow joint and leave your hands soft and in their place.. not jigging or coming upwards when you post.
And just to be clear, I think the problem isn't just hands, but you aren't using your elbows at all.. and if you did, you'd instantly have a happier, correct horse :)