I'm the same height as my bestfriend, but....?

Your body frame and genetics would make a difference. My best friend and I are also the same height, but I know I'll never have the same body shape as her because we are built different. If you want to lose some weight that is ok, but just because she is 70kg doesn't mean you need to be...you just need to be healthy for your body frame (bones, muscle, shape, etc.) I hope that helps. Good luck.