The thing that's illegal is "doing work", not "streaming" or "getting paid". If she does something that people would normally get paid for while she's in Japan, that's a crime, and if you're an autistic Japanese corpo then appearing in a collab is certainly something that could be interpreted as something that someone would normally get paid for.
In practice do they have any way to catch someone doing illegal remote work from Japan? Not really. But again, autistic Japanese corpo, they won't risk breaking the law unless it's to abuse their employees.
