Will God answer the prayer of a girl who has committed a grave sin, which is that her fiancé ejaculated on her anus, and she fears that the fluid may have leaked into her vagina, and can pregnancy occur while she is a virgin?

You must hasten to sincere repentance, for Allah loves those who repent and desires repentance. He has promised forgiveness for sins, no matter how great, to whoever repents to Him and thinks well of Him. Repentance increases the penitent's closeness to Allah and can be a means for answered prayers. It must be noted that an engaged woman is a stranger to her fiancé, and it is not permissible to be lenient in dealing with her, such as being in seclusion (khalwa), going out, or being overly familiar in speech. It is not permissible to speak with her except to the extent permitted by the Sharia. Consult doctors regarding the possibility of pregnancy in such a case.