Is it forbidden to cry and grieve excessively for a mother who passed away in 2005, and to give charity on her behalf with the intention that others pray for her?

There is no harm in the heart grieving and the eye shedding tears at a calamity, so long as it is not accompanied by discontent. Indeed, the eyes of the Prophet, peace and blessings be upon him, shed tears upon the death of his son Ibrahim, and he said: "The eye weeps, and the heart grieves, but we say nothing except that which pleases our Lord." And the son's charity and his supplication for his deceased parents are among the most perfect forms of righteousness. The Prophet, peace and blessings be upon him, said: "When a person dies, his deeds come to an end except for three: ongoing charity, or knowledge from which others benefit, or a righteous child who supplicates for him." And your action is purely for Allah if you intend thereby the Face of Allah, and it is showing off if you intend thereby for people to see and praise you. And you should occupy yourself with your prayers and ponder over the Qur'an and the supplications within them to help you achieve humility.