Advice sought on how to reduce tax liability for senior citizen

Hi, My mother is a senior citizen (71 years old). Her annual income [which is from various FDs in banks] just about exceeds 3 lakhs by a whisker due to which she did not submit the Form 15H. And the bank is now deducting TDS to the tune of approximately Rs 8,000 /= every quarter, which amounts to Rs 32,000 for the year. I have two queries: 1. As per the income tax rule, the rate of tax for senior citizens under the Rs 3 to 5 lakhs slab is given as 10% of the amount by which the taxable income exceeds Rs. 3,00,000/-. Now my mother's annual income exceeds the Rs 3 lakh limit by just Rs 12,000. Does this mean that TDS will be applied ONLY on the Rs 12,000? Why I am asking is because in the TDS certificate [Form 16 A] that the banks are sending every quarter, the tax being deducted is on the principal amounts of the individual FDs. 2. How can my mother avail of the Section 80C to be exempt of all tax liability? For instance, I have a PPF account in my name. Can she deposit the same amount by which her income exceeds the taxable income, in this case Rs 12,000, into my PPF account in March this year? And since the TDS has already been deducted for 2016-17, by when does she have to file a return to get a refund of the tax deducted? Thanks!