Hi Hailey, firstly let me say how lucky you were to transition at 9, and the support you will provide to your friend will be invaluable to her. Oh and you look stunning as should be expected!
Although, as you have already realised your puberty and her transition will be different. She will always be tall, with a medium frame. If she tries to compare how you look to herself, I'm afraid she will be disappointed. There are some remarkably good transitions, but nothing can compare to going through the female puberty like you did.
The degree to how well she will do can come down to several things. Firstly there is her own mental outlook, if she remains positive and applies herself to her transition then she will find happiness. But physically, a fair amount is purely based on luck. The HRT that she will undertake may have remarkable changes to parts of her body, or she may be extremely unfortunate. Until we try, no one actually knows how affective the treatment maybe; so cames the watch words of HRT, Your Milage May Vary.
Physically she might experience all the changes as listed here:
https://www.susans.org/wiki/Hormone_replacement_therapy_(male-to-female)as she is still, young she may have considerable success. I started at 29 and I pass. The one thing I will say is get her to start training her voice now. The voice can absolutely change if you pass or not.
She need to be prepared for a emotionally trying time, there will be a lot of negative experiences and she needs the strength to keep fighting and friends and family who are supportive will help greatly. But as I'm sure you are aware, living as the correct gender just feels amazing, and the reward of that will ( has in my case) make up for the pain.