Which daughter-in-law kissed Naomi goodbye and went back to her people?

Answer: Orpah

Orpah kissed her mother-in-law goodbye and returned to her people and her gods, but Ruth clung to Naomi.

“Again they wept aloud, and Orpah kissed her mother-in-law goodbye, but Ruth clung to her. “Look,” said Naomi, “your sister-in-law has gone back to her people and her gods; follow her back home.””— Ruth 1:14-15 (BSB)