I dont think she is since his mom seems to have a totally dramatic personality and they're keeping the promise to not meet their son until he goes to them. If it is her then damn totally unexpected lol
She almost fly to Japan several times, but her husband and Lory hold her back, and her threat 'I'm gonna die soon' also doesn't work, maybe that's why she is disguised herself to befriend Kyoko, the woman her son likes, though she isn't allowed to met with her son, she could at least see him from afar.
Maybe, I did forget they're a family of actors maybe mum acts too
I think it wouldn't be a stretch if i say she could be Koun's mother. Because their family is a big eater right!? That's why ren got traumatized. This only a theory.. ╮(￣▽￣)╭