No, your sister will not be able to come with your mom. At best, if she qualifies for humanitarian parole, she may be able to come with your mom or shortly thereafter. Otherwise, the wait time for a sibling of a US citizen is about 12 years. Once your mother enters the US as an immigrant and petitions your sister, the wait time would be reduced but it will still be about 6-7 years.
Please let me know if you have any additional questions or if I may be of further assistance to you in this matter.
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