Is it permissible for my wife to pray in her sister's house in Al-Aziziyah, Makkah, to fulfill her vow to pray in the Haram, given that she is unable to go to the Haram due to pregnancy?

Scholars have differed regarding the obligation of immediately fulfilling a vow. The Hanbalis are of the opinion that it is obligatory, whereas the majority of scholars believe it is not obligatory, reasoning that the command to perform the act is absolute and not time-bound. As for the location of the vow prayer, scholars also differed on what is meant by "al-Masjid al-Haram" (the Sacred Mosque) that is specified in a vow: Is it the Kaaba and the mosque surrounding it, or does it include all areas within the Haram (sacred precinct)? The most preponderant view is that the wife should strive to perform the prayer in al-Masjid al-Haram itself as soon as it becomes feasible, as this is more absolving for her responsibility and more safeguarding for her religion.