What we have here is a mismatch.  Taxes are obviously the most important thing in your life right now, and they are obviously not the most important thing in your client's life.  Look at the bright side -- you're not married to each other.  And for me, the worst clients are those that I have to remind, "It's only a tax return."

If their income was less in 2020, put down something for RRC and tell them IRS will figure the exact amount.  It may delay the refund, but they're earning more interest than the bank would pay.  If they complain, remind them "it's only a tax return."