Shinobu Tanaka hasn't been credited in a Nintendo game since 2007. While many assumed she left, people at the
Kyoto Report propose she is now Shinobu Nagata -- a composer who has contributed to Kiki Trick, Brain Age Express, and Brain Age Concentration Training, among others. It's likely she in fact married her Mario Kart composing partner Kenta Nagata and switched divisions at some point from Nintendo EAD to Nintendo SPD. The Wii Play
copyright seems to back this up.
Seems a lot of composers fall in love on the job... Takahito Eguchi & Noriko Matsueda, Hayato Matsuo & Chiyoko Mitsumata, Hajime Mizoguchi & Yoko Kanno, Takayuki Iwai & Yuki Satomura, Kimitaka Matsumae & Manami Gotoh are some others that come to mind.