Malbim: (a) Even though she was Emunah Alei Tola (used to wearing fine clothing - Eichah 4:5), and Chazal said that she was the daughter of Melech Mo'av (Nazir 23b), she agreed to collect like an Oni. (b) She did not want her mother-in-law to collect with her. She was already known in the city to be a wealthy esteemed woman. She agreed to go; people do not recognize her. This is why it says "Rus ha'Mo'aviyah" - she is from a different land, and is not ashamed. She will finance her mother-in-law honorably. She will take only sheaves of Leket, which Aniyim are not adamant about them (if others take them), for there are many fields and everyone collects in a particular field. This is unlike Pe'ah, which everyone grabs from his colleague. The law is, if 99 [Aniyim] say that [the landowner] should distribute it, and one says that everyone will take for himself, we heed him. They take by force. If she will want to take, bitter people will strike her. Also regarding Leket, she said "one whom I will find grace in his eyes" - if I see that he looks at me stingily. I will seek a place until I find grace and will not have disgrace from the harvesters or other Aniyim.

Malbim: She will not go in a vineyard, where there is danger to ascend trees.

Rashi: No. She will find a field of someone who will not resent her [for gathering Leket in his field].