You know that's totally normal. Growing up should also have a clause that says I'm growing up and growing apart. At least you made it out of middle school together! Thats the hardest time. I too love dying my hair, even if its just chalk streaks. It's just fun! Your paragraph also sortof reminded me of when on the Princess Diaries her bff was sooo critical of what she had done as well. Its really normal, but you need to sit down and talk with her and tell her how very much you want her to be your friend, but also be accepting of changes. Everyone likes to try new stuff. Maybe she is scared you may pull away from her? Anyway, just be open and tell her how you feel. HTH
You cannot and will not stop the right thing from happening. But we all can laugh at you while you whine about it.