Can my niece re-enter the u.s again?

She may be eligible. Have her file and if not granted she will need to apply for a B visa at the US consulate.

How long does it take for a background check result to come back for my husbands green card approval ?

Background checks are normally completed within a few months but some take longer much longer.

I received a notice to appear in Charlotte NC for an interview, even though I filed a petition I130 from Mexico. Why?

There may be several reasons involving the petition or it could be an error. What address did you you provide as your permanent address?

How can I change my nationality when I grow up?

If your brother is a US citizen he may petition for you. There may be other possibilities.

Am I eligible to adjust status?

You appear to be eligible to adjust status. Being married to a US citizen permits adjustment even if out of status.

What can i do about my ex lying about his income in court for child support ?

This is not an immigration question. Moving to nother list

If you marry you may petition for her as your spouse. If you become a US citizen you may petition for her as your fiance or if married as your spouse.

My step father petitioned for me will it affect the process if i had a baby? Im not married.

Having a child does not affect your visa eligibility. Marriage may.

Should I upgrade my H1b Transfer in premium or not?

You want to maintain status. The advantage of the premium process is you will have a clear understanding of you status.

F-1 visa renewal through dropbox

It may be approved. The Consulate will determine if you continue to be eligible.