Is it permissible to make up eighteen years of missed prayers while sitting due to their large number?

A woman is obligated to make up missed prayers as long as it does not harm her body or her livelihood. It is not permissible for her to sit during obligatory prayers as long as she is able to stand without difficulty, due to the Prophet's (peace be upon him) saying: "Pray standing; if you are unable, then sitting." A large number of prayers is not an excuse for sitting.