Describing a classmate..

She is a nice-looking brunette of medium height. The first time I saw her was when I started my second year of the course and I remember I thought that she standed

stood out for (or because of) her fashionable style. This girl was attending several subjects (or classes )  with me, but I had never had the opportunity to talk with her before the second term. 

She has a diamond face shape with a smooth golden skin that seems (or appears) to be bathed by the sun. Her hair is, dark, staright and long and most of the time, she wears it in a ponytail or a bun enhancing her fringe. The most noticeable feature of this girl is her sparkling big brown eyes, which give a sensation of inner peace. Her thin lips and her pleasing smile bring an expression of generosity and sociability, difficult to hide. 

Her style is fashionable but casual and relaxed, which gives the impression of an approachable and friendly person. Although before you might meet her, she seems to be very withdrawn and demure, but you would find in her a very talkative and expressive girl who enjoys meeting new people. Her bubbly personality makes her a fun and out-going girl, which is emphasized by her loud and genuine laugh.
In my opinion she is a friendly and sociable girl, which is showed it shown in the way she dresses and in her manners. Even though at first sight she appears to be an introvert, she is cheerful and sympathetic. Her firmness and optimism makes her a confident girl who loves to enjoy life and tries to focus on real things (or things that matter)  and real friendships.


*One of the things that the teacher spot me out pointed out to me was the overuse of verb to be! I hope you can help me with that! Thanks :)

I think Mango has a better correction and I agree that you aren't over using to be.

You write very well !  Thank you for much for correcting my notebook!! 

Describing a classmate.

She is a nice-looking brunette of medium height. The first time I saw her was (I first saw her) when  I started my second year of the course and I remember I thought that she stood out for her fashionable style. She was attending (attended) several subjects with me, but I had never had the opportunity to talk to her before the second term.
She has a diamond face shape with a smooth golden skin that seems to be bathed by the sun. Most of the time, she wears her straight long dark (I wouldn't normally put three adjectives in a row, and as you already said she was brunette you could cut out 'dark' maybe) hair in a ponytail or a bun, enhancing her fringe. The most noticeable feature of this girl  is her sparkling big brown eyes, which (Her most noticeable feature, her sparkiling blue eyes,) give a sensation of inner peace. Her thin lips and her pleasing smile bring an expression of generosity and sociability, difficult to hide. 

Her style is fashionable but casual and relaxed , which (Her fashionable, but casual and relaxed style) gives the impression of an approachable and friendly person. Although before you get to know her, she seems to be very (quite) withdrawn and demure, you would find in her a very talkative and expressive girl who enjoys meeting new people. Her bubbly personality makes her a fun and out-going girl, which is emphasized by her loud and genuine laugh.
In my opinion she is a friendly and sociable girl, which is shown it in the way she dresses and in her manners. Even though at first sight she appears to be introverted (/an introvert), she is cheerful and sympathetic (her cheerfulness and empathy soon come through). Her firmness and optimism makes her a confident girl who loves to enjoy life and tries to focus on real things and real friendships.

I really don't think you've over-used 'to be' at all, but I've tried to suggest an alternative most times you did use it. Your writing is very fluent and you only have about two actual mistakes, but I've suggested  some other things that might make it seem slightly more natural, like cutting out word you don't actually need or changing some, but mostly that's up to you. Hope that helps and my corrections make sense :)