Income from rent paid by builder for redevelopment

My mother (Age 78 yrs) owns a flat in Mumbai. The building is under redevelopment. The builder has paid her 11 months rent of Rs 370,000/- in advance and corpus money of Rs 9 lakhs. She has no other income except some small amount of interest on Bank deposits.

Whether she will have to declare the rent and corpus paid by the builder and if so, which ITR Form to submit? Is corpus money also taxable?