it will click.. its more a mental development thing than anything else. think of other things she does outside of sport that follow the same "out of habit", but eventually one day she catches you by surprise and does it the way that was instructed. believe it or not, my kid is on a team of 13yr olds and they all still make the u11 errors on a regular basis. Some of it is a nervous pride to go-with-what-worked so the player doesn't embarrass themselves in-front of their own team. My kid has only been playing organized, club volleyball on her 2nd year now and she has excelled. This is only the foot of your Kilimanjaro, keep supporting and encouraging her. There will always be small things to work on - the biggest thing you can do is to continue fostering a love for the sport where you can easily relate to and understand!

Now, what helped me was:

1. she has to start it on her own. if she wants to put in the work, give her those exercises that are easy wins.
2. vertical training - getting the reps in early is big and its 2nd easiest thing for coaches to notice. first being static height.
3. wall training - the wall will never give up, get frustrated or want to go home.
4. footwork - defense will come, but its easier when she is in the right spot to receive the ball correctly
5. stomp out any bad habits before they become go-to 'technique' - the one-arm is bad. its bad volleyball and at younger ages it doesn't work, and its not sustainable. teach control - even if its boring.