Must one make up missed prayers for not knowing they were obligatory, or for living in an environment where it was difficult to commit to prayer? And must my mother make up her missed prayers for the same reasons?

Prayer is the pillar of religion, and abandoning it is a grave sin. A Muslim is not excused for abandoning it due to ignorance or social courtesy. Scholars have agreed on the disbelief (kufr) of one who abandons prayer out of denial, but they have differed on the disbelief of one who abandons it out of negligence. The three Imams (Abu Hanifa, Malik, and Shafi'i) believe that such a person is not a disbeliever and must repent and make up the missed prayers. Imam Ahmad, however, believes that such a person is a disbeliever and must repent without making up the missed prayers. It is obligatory to repent and make up the missed prayers as much as possible. It is not permissible to reside in non-Muslim lands if a Muslim cannot practice the rituals of their religion. It is also not permissible to sit in gatherings of disbelief or where Allah is insulted, for Allah Almighty says: "And He has already revealed to you in the Book that when you hear the verses of Allah denied and ridiculed, then do not sit with them until they enter into another conversation. Indeed, you would then be like them."