Grandma received a letter from it dept.

Hi, My grandmother received a letter from the IT dept. saying she had not filed the IT return for the financial year 2013-14. And asked for a response for the same in 20 days. Her income is only the interest from FD every year. Doesn't cross any slab. But last 2 years she forgot to file form 15H with the bank so they kept deducting TDS. So what should she do about this? Also, the letter is dated February but it was received only today. So I suppose I should count the 20 days from today? Pls help and advice.