The fact seemed to be that, after her mother, Onshi, died, she felt lonely, and had affairs with Morosuke whose wife, Imperial Princess Masako (or Gashi), had just died, before the official procedures for marriage took place, and "Okagami" (the Great Mirror) introduces an episode where FUJIWARA no Saneyori revealed her unprincipled behavior in front of her younger brother, Emperor Murakami.
実は、母・穏子が没すると身辺が寂しくなったらしく、同年に妻・雅子内親王を亡くしたばかりの師輔と正式の婚儀を経る前に懇ろになってしまったのが事実のようで、『大鏡』では弟・村上天皇の面前で藤原実頼にその節操の無さを暴露された話が紹介されている。