Being diabetic your mother having chest pain could be because of heart problem as the doctor told it is blocked 2 arteries & third also.Was the doctor a Cardiologist?.I guess he was.Anyway for heart to find out the blockage the investigations are:-
--ECG ;it will give you an idea of the heart whether there is a heart attack
or reduced supply of blood.
--CPK-MB is the enzyme test done in acute chest pain
& is diagnostic of a heart attack.
--A perfect idea of block comes from ANGIOGRAPHY
;it is done by Cardiologist and it gives a idea of how much is the block in each blood vessel.
After this the Cardiologist will give treatment with medicine or may suggest a ANGIOPLASTY
to correct the blockage
Please consult a Cardiologist