I need to know if I can bring my step daughter from El Salvador to California legally, behing I'm from U.S.?

Not without going through the INS with all the required paperwork and fees... and expect it to take a lot of years.

You would have to be her sponsor... she's not a US citizen... and none of here birth paretns were... as she is only a step daughter.

You can file CR1/CR2 for both your spouse and step daughter at the same time if she is under 21 years of age. Waiting period will be the same for both, approx 10-12 months.