Is a mother who suffered psychological problems due to the hijab, affecting her mental faculties and religiosity, considered among those for whom the pen has been lifted?

The basis of accountability (taklif) is reason, so when reason is lost, accountability ceases. Whoever loses their reason due to fainting, senility, or insanity is absolved until they recover. This is supported by the Prophet's (peace and blessings be upon him) saying: "The pen has been lifted from three: from the child until he reaches puberty, from the sleeper until he awakens, and from the insane until he recovers." Therefore, if the mother has lost her reason, the pen is lifted from her as long as she remains in that state. If her reason returns, accountability returns to her. Your dutifulness towards her in these circumstances carries a great reward and is a means to enter Paradise.