Other sources talk about her probably taking an overdose of tranquilizers. The doctor had prescribed a certain dosage to her, but it seems that she took much more at once than it was prescribed:
http://www.tokyograph.com/news/id-4315
http://www.sanspo.com/geino/news/090...0120003-n1.htm
I don't know much about her. I don't think I've listened to any song by her..not sure. Well, sad to see she's not well though
It seems like she had attempted suicide a couple of years ago too:
http://www.tokyograph.com/news/id-1296