What is the ruling on holding oneself accountable for shortcomings towards parents after their death? And does seeing the mother in a dream, and her advising one to pray Fajr daily in the mosque, increase her pleasure after Allah's pleasure? And will she be rewarded for that?

Regret over shortcomings towards one's mother is a good sign and a sincere repentance. Holding oneself accountable for mistakes is a great act of obedience. Shortcomings are expiated by sincere repentance, frequent seeking of forgiveness (istighfar), praying for her, giving charity on her behalf, and honoring her friends and relatives after her death. It is not permissible to abandon good deeds due to regret, as this is a whisper from Satan. Not kissing the parents' hand is not an act of disobedience (uquq). Allah forgives the transient slips of a dutiful child towards their parents. The intention behind any action must be solely to please Allah. The deeds of the living are presented to the deceased. The mother receives the reward for the good deeds she encouraged during her lifetime, and this does not apply to what appears in dreams after her death.