What can i do if my pay is unfare?

i've been working in this place for more than two years, and this girl who used to worked there is back and was off for more than three years, the thing is that she earns more money than me and she doesn't do anything i don't think that's fare and my boss is really bitchy what can i do help!!!
...............................................................................
Do both of you have exactly the same job title?

Option #1:
Discuss the situation with your HR Manager.
Be prepared to explain in detail why you feel you should get a raise so that your pay equals the pay of the other employee.

Option #2:
Look for another job.
...............................................................................
Maybe this girl has a lot more experience than you do.

If you are unhappy with the pay rate, Human resources is the department you need to speak with. Keep in mind that not everyone is always paid at the same rate, and in this economy, a job with a slightly lower pay scale might be much better than no job.
...............................................................................
Talk to Human Resources. Ask them to re-evaluate and compare you to her on the basis of performance and seniority.