Torah Temimah citing Shabbos 113b: Rus kept coming and going until she found proper people to go with them.

Rashi citing Rus Rabah: She made signs on the roads before entering the field and returned to the city, lest she err on the paths and [not] know how to return.

Vilna Gaon: She went in the entire field without gathering. Why should she carry a heavy load back and forth? After reaching the end of the field, she returned and gathered until the city.

Malbim: She did not need to go far. She immediately came to Bo'az' field and began to gather, for it was near. Even though it was morning, which is one of the three times that they give out Pe'ah ¹ (Pe'ah 4:5) in the corner of the field, she did not go to there. She alone took Leket (the other Aniyim were taking Pe'ah).

Rashi: She happened to come to Bo'az' field.

Malbim: Mikreh is something without a cause that makes it occur; it is due to Hashgachah. R. Eliezer requested "Hakre Na Lefanai