A Muslim woman should try her best to stick to the teachings of Islam and abide by the Islamic decorum, especially when dealing with people of the opposite sex.
“Whoever is killed in defense of his property is a martyr, whoever is killed in defense of himself is a martyr, whoever is killed in defense of his religion is a martyr, and whoever is killed in defense of his family is a martyr.” (Ahmad and Ibn Hibban)
However, she is not allowed to kill herself under any circumstances because suicide is prohibited. The only One Who knows the Unseen is Allah. She never knows what will be the outcome of their criminal attempt; they may fail in carrying out their devilish plan.
Here we can imagine the occurrence of two harms, one of them, relating to suicide, is certain, while the other, relating to her being subjected to rape, is something possible, but not certain.
Thus, in this case, committing suicide is not permissible.
Moreover, we have to weigh the harmful effect of suicide to that of rape or sexual assault. The latter is endurable unlike the former.
Besides, preserving one’s soul is among the necessities of life, whereas other objectives, such as preserving one’s chastity, come in the second degree among the fundamental goals that Islam is keen to realize.
Thereby, it is not permissible for a woman, a victim of rape, to commit suicide.
Sources: IslamOnline Archive