How to show source of money, from sale of farmland?

My mother sold her village ancestral farm land recently. She received 45 lac by check and 21 lac by cash. Unfortunately, buyer wanted to buy with circle rate and rest of money, he gave as cash. Her SBI account is already having 28 lac and now she got 45 lac also via sell of this farmland. Now painpoint is this 21 lac, how she is going to deposit it. We don't want to attract any tax or penalties. Will it be asked what is source of this money and can go into complication?
It is common in village to get money cash for seeds, crops, etc., but showing that above 5-6 lac may look little unrealistic.
Please advice.
Thanks