Her grandmother is late 70's, but she is still working and make enough money. Could this work? Or is there an age restriction?
The only age restriction applying to a Joint Sponsor is that they must be 18 years old and live in the United States or a U.S. territory or possession. By the way, even though your wife does not make enough on her own to qualify, she still is the primary Sponsor and your her grandmother would be a Joint Sponsor.
I recommend consulting with an experienced immigration lawyer to explore your options.
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