"be equal to her 3% as a beneficiary"

What 3%?

If your client got a portion, that FMV and any Basis would carry over.

$100,000 FMV, $20,000 basis = 20% basis.

Your client gets 3% = $3,000 inherited, and the first year, assuming in this example no growth or earnings, then Basis is $600. $2,400 would be money that was never taxed. That matters when there is a distribution, to not double-tax basis.

The Broker should be able to help, and the tax software should handle the rest.

This never should have been this hard.