Yee she can get the refuge certificate if the record is intact

Section 6 of Indian citizenship act provides 

person who has migrated to the territory of India from the territory now included in Pakistan shall be deemed to be a citizen of India at the commencement of this Constitution if—
(a) he or either of his parents or any of his grandparents was born in India as defined in the Government of India Act, 1935 (as originally enacted); and
(b) (i) in the case where such person has so migrated before the nineteenth day of July, 1948, he has been ordinarily resident in the territory of India since the date of his migration, or
(ii) 

in the case where such person has so migrated on or after the nineteenth day of July, 1948, he has been registered as a citizen of India by an officer appointed in that behalf by the Government of the Dominion of India on an application made by him therefor to such officer before the commencement of this Constitution in the form and manner prescribed by that Government:

3) your grandmother should be a regarded as Indian citizenship but need evidence of such migration 

A person can acquire citizenship by naturalisation if he/she is ordinarily resident of India for 12 years (throughout 12 months preceding the date of application and 11 years in the aggregate) and fulfills all qualifications in the third schedule of the Citizenship Act.

Persons domiciled in the territory of India as on 26 November 1949 automatically became Indian citizens by virtue of operation of the relevant provisions of the Indian Constitution coming into force, and most of these constitutional provisions came into force on 26 January 1950. The Constitution of India also made provision regarding citizenship for migrants from the territories of Pakistan which had been part of India before partition.

You may have to look for the documents which may be available with the immigration department.

Dear Cleint ,

Persons domiciled in the territory of India as on 26 November 1949 automatically became Indian citizens by virtue of operation of the relevant provisions of the Indian Constitution coming into force, and most of these constitutional provisions came into force on 26 January 1950. The Constitution of India also made provision regarding citizenship for migrants from the territories of Pakistan which had been part of India before partition.

Citizenship of India by naturalization can be acquired by a foreigner (not being an illegal migrant) who is ordinarily resident in India for twelve years (throughout the period of twelve months immediately preceding the date of application and for eleven years in the aggregate in the fourteen years preceding the twelve months) and fulfils other qualifications as specified in third schedule to the act, 1955

If she have some record that she was residing in India at time of formation of constitution then she is deemed to be citizen of India. 

Or she can apply for refuge certificate in department of records.