What is the ruling on a person with some mental health issues not making up missed fasts?

If the mental issues take their owner beyond the limits of taklif (religious accountability), such as by becoming insane or similar, then the religious obligations fall away from her, and she is not obligated to fast, neither by performance nor by making up. However, if she experiences periods of insanity and periods of lucidity, then she is not required to make up the day during which she was insane, but she is required to make up the days during which she was lucid. If she becomes insane during a day when fasting is obligatory, and she had already formed the intention for fasting, then the relied-upon view among the Hanbalis is that she is not required to make up that day. Sheikh Al-Uthaymeen, may Allah have mercy on him, said that a person who has lost their sanity is not accountable, and nothing is obligatory upon them at all, citing the hadith, "The pen has been lifted from three." However, if the mental issues do not take her beyond the state of being considered rational, then she is addressed by religious obligations.