Woman speaking aloud in prayer in the presence of her mahrams

It is permissible for
a woman to say Ameen out loud, if she is in the presence of her mahrams
and there are no “strangers” (non-mahram men) present, because a woman
is forbidden to raise her voice in the presence of non-mahram men for
fear of fitnah (temptation). But in the presence of her mahrams she
is not forbidden to do so. 

Shaykh
al-Fawzaan (may Allaah preserve him) was asked about a woman speaking
aloud during prayer, and he said: 

It is mustahabb for her to recite out loud in prayer,
whether it is fard (obligatory) of naafil (supererogatory) (i.e., the
prayers in which Qur’aan is to be recited out loud), so long as no non-mahram
man can hear her, lest he be tempted by her voice. But if she is in
a place where no non-mahram man can hear her, then in prayers offered
at night she should recite out loud, but if that will disturb others
then she should not recite out loud. But in the case of the prayers
that are offered during the day, she should recite silently, because
the prayers during the day are to be recited silently. So it is not
mustahabb to recite out loud in the prayers that are offered during
the day, because that goes against the Sunnah. And Allaah knows best.