The woman was surprised to find a carry bag in front of her house and when she opened it she found the petrol bombs (bottles filled with petrol and attached with fuse wires), police said.
She found a letter inside, which thanked her for supporting an organisation (which was not named) all these days, police said.
Police took possession of the bag, they said, adding, the woman, her brother-in-law and two others in the area are being questioned.