If you are at least 21 years old and if your mother is outside the United States, you need to first petition for a nonimmigrant visa for her by filing a Form I-130 and submitting the necessary fee and documents in support of your petition. If your petition is approved, you will be notified, and your mother will be asked to go to the U.S. consulate designated by you in the I-130 petition to complete her visa processing. This includes completing other forms, visiting approved physicians for tests, and submitting additional documents. You will also need to submit an affidavit of support -Form I-864 - and documents in its support. For further information, see, http://www.uscis.gov.
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While your mother is still on a visit to the United States you can file Application for Adjustment of status. If she is outside the US you will have to file Petition for Alien relative. All things being equal it takes less than a year. Get a Lawyer.