please correct my grammar?

Jean is a 20 year old fire fighter from Westchester, New York. She is also a student and a part-time model, and can sing and act. She loves being in front of the camera.

Jean is interested in a full-time career in modeling. Her Italian, Irish, Polish, and Greek heritage give her a unique look.

Okay, I did a little more than correct your grammar. You can't "break into" what you're already in, and you said she was a model. Things can be "very unusual" or "unique", but not "very unique" (although you see it a lot) because "unique" means there's only -one-. And if you're writing in the third person ("she"), you shouldn't suddenly break into first person ("I").

Jean is a 20 year old model and a fire fighter from Westchester, New York. She is also a full-time student, and I can sing as well as act. Jean is interested in breaking into the modeling industry and making it her full-time career. She loves being in front of the camera. She has a very unique look. She is of Italian, Irish, Polish, and Greek extraction

Just two small changes and it reads clearly, grammatically and well.

Jean is a 20 year old model and a fire fighter from Westchester, New York. She is also a full-time student. She can sing as well as act. Jean is interested in breaking into the modeling industry, making it her full-time career. She loves being in front of the camera. She has a very unique look. She is Italian, Irish, Polish, and Greek.

Jean is a very unique person. Of Italian, Irish, Polish and Greek background, she is multi-talented. She can sing, act, loves being in front of the camera, and is interested in becoming a full-time model. At 20 years of age, she currently models, is a full-time student, and a fire fighter in Westchester, New York.

Jean is a twenty year old model, singer and actress, and a fire fighter from Westchester, New York. She is also a full time student. Jean is interested in breaking into the modeling industry and making it a full time career. She loves being in front of the camera. She has a very unique look, due to her Italian, Irish, Polish and Greek ancestry.

Jean is a twenty year old model and firefighter from Westchester, New York. She is also a full time student, and can sing as well as act. Jean is interested in breaking into the modelling industry and making it her full time career. She loves being in front of the camera. Jean has a very unique look - she is Italian, Irish, Polish and Greek.

The one most important change is in your person.

You start by talking about Jean. Then you say "I can sing as well as act" instead of "she can sing..." and "making it my full-time career" instead of "making it her full time career" since you talk about it as if it is some one else.

If you are Jean, you could replace the "Jean"s making it personal, as in the following:

"I am Jean. I am a 20 year old model and a fire fighter.... I am also a full time student and can sing and act...."

This example switches between first-person and third-person several times. It also is a bit wordy. The overuse of the word 'and' is a minor problem, as is the overuse of the person's name (which is acceptable in a performance review).

One could also consolidate a few of the sentences to make the reading of the paragraph more pleasant.

are you talking about Jean or yourself?