Should I Tell Her?

Hello Everyone.
I have a strong crush on 15 year's old girl which is my best friend's sister and i am 19 year's old.
I have crush over her from around 6 months. She always do what i say (example in my street there was boy who was chasing her i told her to stay away from him so she did exactly same as i had said her)
She has a different behavior with me among our group of friends but sometimes she call me as brother. But i have literally strong crush on her.
So should i chase her or not?
Should i say i like her?
Please give opinion.
Thank You.
Should I Tell Her?
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