I pray to Allah to console your heart, inspire you with patience in accepting the will of Allah, and forgive your beloved mother.
Death is the destiny of every living being. No one including the great prophets and messengers was exempt from it. Allah says in the Qur’an: “Every soul shall taste the cup of death…” And the Prophet (peace be upon him) is told to say to those who vowed to kill him: “We never decreed immortality for anyone before you. So, if you were to die, will they live forever?” (Qur’an: 21:34).
Therefore, I would urge you to console yourself by remembering the death of the Prophet (peace be upon him). Remember his high station with Allah. When his turn came, he surrendered his soul peacefully. His death came as a shock to his companions as they loved him more than anyone else in this world. That was why even eminent companions like Umar denied his death until they came to senses when Abu Bakr addressed them saying: "If anyone has been worshipping Muhammad let him know that Muhammad is dead. If however, anyone has been worshipping Allah let him know that Allah is EverLiving and will never die.”
So, console yourself by saying: "We all belong to Allah and we are destined to return to Him.”
Therefore, I would urge you to drive away the Satanic whisperings by directing your mind to pray for your mother. By doing you are benefitting the soul of your mom. If on the other hand, you continue to weep over her death, it would do no good to you or her; rather you end up committing the sin of failing to accept the will of Allah.
As for your worry about her state with Allah, all that you can hope is to know that Allah is Forgiving and Merciful; so let us pray that He treats her with His Infinite Mercy.
You may also think of doing some good deeds on her behalf. On further details, please refer to the answer linked below.