Answer
Wa`alaykum as-salamu wa rahmatullahi wa barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear sister in Islam, thanks for your question, which emanates from a God-fearing heart, since it shows your commitment to Hajj, one of the five pillars of Islam.
The Prophet (peace and blessings be upon him) said, “Islam is built upon five pillars: testifying that there is no true god except Allah and that Muhammad is the Messenger of Allah, performing Prayer, paying the Zakah, making the pilgrimage to the Sacred House (Hajj), and fasting the month of Ramadan.” (Al-Bukhari)
In response to your question, Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states,
Your mother may wear diapers during the course of Hajj, should it be considered necessary for her.
There is nothing in the authentic sources to indicate that it is unlawful for her to do so while in a state of ihram. Restrictions that are applicable to male pilgrims in this respect do not apply to women, as they are allowed to wear all sewn clothes except gloves and face-veils.
Therefore, she is allowed to wear a diaper without breaching any of the rules of ihram applicable to women; hence there is no need for her to offer a fidyah (compensation) for violation.
Allah Almighty knows best.
Excerpted with modifications from www.muslims.ca