On the other hand, the building they're in is not the best at keeping its signage up to date. And older people know it with the Ellen in the name. So I'm not sure about that part - it's probably ok to keep it as "Ellen Masaki".
But..."Ward Ave, 2nd Floor" is not very specific (there are a lot of buildings on Ward Avenue). The building where the school is located is called Ward Court, located at 250 Ward Avenue.
So maybe "Ellen Masaki School of Music, Ward Court Bldg. (250 Ward)"?
What do you think - is that worse than what's there now? :s