Any tax to be paid for ancestral gold sale?

My mother is 72 years old and she sold her ancestral gold for 20 lakh in March. She got the receipt also from Jeweler and he gave her check, which was deposited in her account.
Now at time of tax filing, I am seeing conflicting answers, if she will need to pay anything.
- I am reading in some blogs that, if she invest this 20 lakh in govt bonds, she won't have to pay any tax under 54ec.
- Other blog says gold sale was removed from 54ec, so if there is no buy price known (it is ancestral since more than 70 years), gold price of 1st April 2001 will be considered and as per index on capital gain, taxes needs to be paid.
- Another say that within some months of gold sale, same money can be invested in govt bond and that will avoid any taxes.
- Or there should not be any tax paid on this? He mother's mother gave her that gold.
Please advice, if taxes can be saved on this sale.
Thanks