I can read the notes

It does take practice. That is how your mother got there. With practice. When she was younger she was probably very similar to you in how she learned. You just have to be patient and wait, and never stop learning! Also, never compare yourself to someone who you know is better, because that is the same thing as putting yourself down, just not in a direct way.

I have the same problem as you but and i don't have a teacher but I think I will just practise some more.

Reading is a skill, the more you work at it the better you get. I think I'm a better overall piano playr than my late sister was, but she by far blew me away sight reading. Well, most people blow me away with sight reading...I can only limp along because of my composing activities, which keep rhythmic notation and the notes fairly fresh in my mind. But it's really a choice of mine. I'd rather spend time playing the piano and improvising, and eventually composing a piece, THEN start the process of writing it down. My sister was the opposite - she never cared about composing, but loved to play. Hence she work a lot harder than I ever did to sight read. And as others have said, it's not a skill that just appears. It takes a lot of hard work to get to a high level. And I agree - it's not good to compare yourself to a superior player and get down on yourself. Try to use your mom's skill as a motivation to get better. If I let all the piano players I've seen and heard that are better than me get me down I would have given up, oh, by the time I was 8 maybe.

Hey Dan! Is your mom the one that taught you piano?

I can play both hands right away, but I have to do it VERY SLOWLY. My mom is an experienced piano player as well, and she can read pretty much anything that's put in front of her up to tempo. However, she has been playing and teaching for many, many years. It takes most people a long time to develop their skills enough to read everything at first sight. There are exceptions, but most people have to work very hard to get to the level that your mother (and my mother) is at.

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Just keep going. You'll be great.

First of all don't get discouraged! Most people can not play right away. It takes ALOT of practice. Also, try not to compare yourself to other people and stay focused on you. Are you taking lessons?