Does the Japanese citizen family member income sponsor have to be currently residing in Japan? (For spouse visa)

I'm the Japanese citizen and have a Finnish spouse, we are looking at possibly immigrating to Japan but would not fulfill the income requirements. My Japanese citizen mother who would be likely to be an income sponsor does not currently reside in Japan as she is on a green card living in the US with my father. Would this disqualify her and would I need to find another family member to be an income sponsor that currently resides in Japan?