What can I do to help my grandmother, the doctors say she isn't gonna live for more than a few more days?

It is mustahabb to exhort the dying person to utter the Kalimah or word of faith in this situation, so that his life will end with that and it will be the last words that he utters. Hence the Prophet (peace and blessings of Allaah be upon him) enjoined it. It was narrated that Abu Sa’eed al-Khudri (may Allaah be pleased with him) said: the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Exhort your dying ones to say Laa ilaaha ill-Allaah.” Narrated by Muslim, 916.

It was narrated that Mu’aadh ibn Jabal (may Allaah be pleased with him) said: I heard the Messenger of Allaah (peace and blessings of Allaah be upon him) say: “If a person’s last words are Laa ilaaha ill-Allaah, Paradise will be guaranteed for him.” Narrated by Ahmad, 21529; Abu Dawood, 3116; classed as saheeh by al-Albaani in Irwa’ al-Ghaleel, 687

Make sure she has no debts,

Reciting Qur’aan over the deceased after he has died is a bid’ah, unlike reciting for the one who is dying.

Majority of the scholars agree that it is mustahab to recite Yaseen over the dying person.

Let her pray a lot and recite quran.

Tell her to be patient and endure it

Anas narrates: “I heard the Prophet (s) saying: ‘Allah says: “When I afflict a servant of mine with respect to his two most beloved things (meaning his eyes), and he endures it patiently, I grant him paradise in return‘.”

Al-Nawawi said:

"The sick person should strive to have a good attitude and avoid arguing and disputing concerning worldly matters. He should bear in mind that this is the end of his time in the realm of deeds, and he should end it with good deeds. He should seek the forgiveness of his wife, children, all his family, neighbours and friends, and all those with whom he had dealings or with whom he was friends or had any kind of connection, and ensure that they hold nothing against him. He should focus on reading Qur’aan, reciting Dhikr, and reading stories about the righteous and how they were at the time of death. He should observe regular prayer and avoid impurity (najaasah), and take care of other religious duties. He should not accept the advice of those who try to turn him away from these things, for this is something with which he will be tested, and this person who tries to do this is an ignorant friend and a secret enemy. He should advise his family to bear his loss with patience and not to wail over him or to weep excessively. He should advise them not to do any of the bid’ahs (innovations) that are customarily done at funerals. He should ask them to make du’aa’ for him. And Allaah is the Source of strength."

I've been a similar situation; my father was very sick, he had cancer and doctors said that he will die soon and it's just a matter of time.

i had faith that Allah can heal him no matter what doctors said; so i prayed for him, made charity, read quran on him and on zamzum water and wiped his body everyday,etc.

but 3 weeks later and he passed away, Allah yrhamo.

keep making dua' and ask Allah to heal her and to ease her death if her destiny is to die, do charity, wake up at the final third of the night and pray, ask Allah to make a hoson khatima for her.

EDIT: btw i was telling my father everyday to repeat the following words: ashhado ana la ilaha ella Allah wa ashhado ana mohamadan rasol Allah, astghferfo Allah wa atobo elay, al7amdolilah, la elaha ella anta subhanaka ani konto mn el thalemeen.(and sometimes he was repeating quran after me) it's very important.

and don't forget to read surat yaseen in the time of sakarat el mwat to ease her dying moments...

May Allah help you and heal her

If she is able to, wake her up in the later part of the night and just the two of you and pray Salaat al Layl (tahajjud prayers).

Her time has come and evidently she has had a good and long life to have her grand kids around. Just being there is good, this is all that is needed. She is in peace.

Take her to a better hospital. No doctor can predict a patient's expiry date. Only Allah(SWT) knows.

Read this Surah AT-Taubah 128 & 129 direct it to her..

& Also Ayatul Kursi..

InshakAllah..

Encourage her to continuously recite "La Ilaha Illallah" and do so yourself while you're with her.

EDIT:

See Amallay's answer below, which explains this in more detail.

Talk to her and make her laugh as much as you can.

She'll die peacefully if she's a happy woman in her final hours.

Dua