While prostrating in Prayer the woman should keep her limbs close to her body, and not spread them out, because this is more modest and covering. (Al-Mughni, 2/258)
Al-Nawawi said: “In his Al-Mukhtasar, Ash-Shafi`i said that there is no difference between men and women in Prayer, except that women should keep the parts of their bodies close to one another, and they should make their stomachs touch their thighs during prostration. This is more covering and preferable in bowing and the rest of the Prayer as well.” (Al-Majmu`, 3/429).