With the sale agreement and allocation, the lawyer's statement of funds, the deposit record, tax filings for the relevant years, and the records showing how she acquired and built the practice in the first place.
Trace the sale, then trace the practice
Proceeds of a professional practice sale are lawful capital, but USCIS requires the path and the origin. For a Torbay dentist the file begins with the agreement of purchase and sale for the practice, the schedule allocating the price among goodwill, equipment, leaseholds and receivables, the closing statement from the lawyer showing net proceeds after debts and fees, and the bank record of the deposit. It continues with the tax return reporting the sale and the returns for the preceding years showing the practice's income.
It then goes back further: how was the practice acquired? If purchased, the original purchase agreement and how that purchase was funded, whether by a professional loan since repaid; if built from scratch, the incorporation records, early financial statements and the loans or savings that started it. Perfect records from twenty years ago are not expected, but the story must be coherent and the large steps documented.
The wire from the dentist's account to the enterprise, in her own name, completes the path.