Albert Barnes Commentary Deuteronomy 21:14

"And it shall be, if thou have no delight in her, then thou shalt let her go whither she will; but thou shalt not sell her at all for money, thou shalt not deal with her as a slave, because thou hast humbled her." — Deuteronomy 21:14 (ASV)

Thou shalt not make merchandise of her - Rather, you shall not constrain her: literally “treat her with constraint,” or “treat her as a slave.”