Why does my best friend copy me?

I have known my best friend for about 12 years and I dont know what I would do without her. But recently, I’ve noticed that she is like slowly turning into me. If I say that I like something in a shop she will like it too and will buy it. Whenever we go out, we’ll end up in very similar clothes, so people assume we are either continuously joined at the hip or are sisters. She had her hair cut in a similar way to mine too. One time for example, we went shopping and I saw a jumper that I liked but because Id just bought some leggings ( which she also liked and had bought too) I didnt have enough money left. But as it was coming up to xmas I tried it on anyway so I could tell my mum about it and she could buy me it later. She (of course) decided to try it on as well. But as I really wanted it I had to lie and say that I didnt like it when I tried it on to try and put her off because I knew that if I said I liked it she would get it. I really hate people wearing the same things as me as I like to be unique and stand out from the crowd. Even though, we are both only children, my parents dont spoil me that much because they have always taught me that money isnt everything and that if I want something enough I should get it by earning it. She always has more money than me so when we both passed our GCSE English exam and I got a A, I was rewarded with a Miss Selfridge scarf and some other nice things for all my hard work. But she had to get something more expensive. I know that I should be flattered and I am, and I know that Id hate to upset her but what can I do? :) x