Recovery of Excess Family payment of Rs. 313000 by SBI

Respected Sir, My father was in CRPF as a head constable. He died on 25/04/2006 due to a heart while he was giving training to new recruiters. Sir, My mom is getting family pension w.e.f as per the enhanced family pension scheme from 25/04/2006 for a period of seven yrs. Sir, now she got a notice from SBI that she is getting enhanced pension from 01/04/2013 to 30/11/2015, so as per her pension book she is liable to get enhanced family pension till date 31/03/2013. Now the bank noticed her that she have to pay Rs. 3,13,000 as excess pension credited to her account. My mom totally depend on her pension as she also a heart patient and have problem in her legs and can't walk properly. She have no deposit in his account. It is very difficult for us to manage a lump sum of Rs. 3,13,000 in a month. I want to know sir, are we legally force to pay lump sum of Rs. 3,13,000 within a month or there is any option to deduct a monthly installment from her pension without interest or as advised by SBI manager to take a loan of Rs. 3,13,000 to pay the recovery of excess payment. Sir, I mom is in hardship of her health problem. Kindly suggest me what action/way I choose