No one can answer whether or not she will get an approval. But let's assume that everything is in order and she has no in admissibility issues and the only snag is your income, then yes if brother is a co sponsor then she should eventually get her visa.
The answer provided is general in nature and should not be construed as legal advice as not all facts are know by the attorney, nor does the answering of this question create an attorney client relationship.
It depends on how many people your brother is supporting. You also do not say what about your income is "no good." You only need to show that you are 125% above the federal poverty line. For three people it is only $19,090. See, http://aspe.hhs.gov/poverty/12poverty.shtml#guidelines You likely need the assistance of an immigration lawyer.
The herein content is for general informational purposes only, and may be predicated on incomplete facts. It should not be relied upon in making legal decisions or assessing your legal rights or risks. Neither does the herein reply create an attorney-client relationship.
Visa approval depends not only on the affidavit of support. As to your brother's income, it depends on the size of his family and his reporting practices. Consult with an attorney.
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