Why I didn't stand up?

At my bus, there is a girl who has down syndrome. People from my bus stop have bugged this girl a lot and I feel uncomfortable about it. But, once she was acting funny but my friends didn't think. So, it gets on my friends' nerves. But in my opinion, he was supposted to just leave her alone. But, he didn't. He kept messing with her. I didn't do anything. After I got home I mentioned this to my mom and grandmother. They told me that I shouldn't just be silent and be friends with the girl.She is a human like us, and I should of have talked to my friend to change what he did and thinks about teh down syndrome girl.Today I still keep questioning myself why....why.... I didn't stand up and did something.....