How many months should we wait?

My Mom was granted for another 90days extension here in Japan and that extension will end this month so she will go back to philippines but we are planning again to invite her for a visit as soon as possible. How many months should we wait before we can apply again? Thank you.

As long as she gets her visa renewed, she can come back to Japan anytime she wants to. But renewals of visas vary greatly depending on the individual and their citizenship. I hope this information gives you somewhat of a clue. https://www.us.emb-japan.go.jp/itpr_en/travel_and_visa.html