If either you or your sister are US citizens you can petition for your mother to get a Green Card. The entire process should take 9 months to a year before she arrives in the US.
Samuel Ouya Maina, Esq. 415.391.6612 firstname.lastname@example.org Law Offices of S. Ouya Maina, PC 332 Pine Street, Suite 707 San Francisco, CA 94104
My colleague is correct ... if one of you is a US citizen ... that person can file an I-130.
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If you or your sister are US citizens one of you can file am I-130 Application for your mother and should be able to come within a year or so if there are no issues or problems that I am not a aware of. Good Luck!