Keeler was generous with the two strange men, as she was generous with all of the unfortunate people who sought help from her.
Kirk and Spock worked for her (NOTE: answered to her, took orders from her) at the mission for 10 hours a day, and were paid (by her) 15 cents an hour - which was a living wage in the Depression-era USA. This money made it possible for Spock to buy the radio tubes and etc. that he needed to complete his mission. If not for Edith Keeler, they might not have succeeded at all.
We learned from this episode that Edith Keeler was an intelligent, and amazingly far-sighted woman, who in one possible timeline was destined to play a huge role in historical developments. Inspired, dedicated, eloquent, charming,elegant and persuasive, she was to win the ear of the US President, and would lead a hugely influential peace-movement, which would delay the USA's entry into the second world war.
Jim Kirk didn't know all that when he first became acquainted with her. He was attracted to her both because she was lovely, and because he very much appreciated her mind, and her soothingly elegant manner.
Contrary to how it was in Kirk's other "romances", Kirk was under no extraordinary influence that made him imagine he had feelings for her, and he had no ulterior motive behind his courtship maneuvers: he honestly simply seems to just love her. And why not? She was shown to be intelligent, far-sighted, hard-working, saintly, sweet, understanding, charming, noble-souled, faith-filled, intelligent, imaginative, forgiving, helpful, strong-willed, clear-headed, powerful, beneficant, feminine and gorgeous - with leadership capability and enormous socio-political potential. What's not to love?
Only after Kirk has fallen in love with Miss Keeler is it revealed that Miss Keeler must die to restore Kirk and Spock's timeline.
Miss Keeler's one human life held the fate of two whole universes in the balance, which makes her one human life incalcuably important to God knows how many lives.
Edith Keeler is the only woman in all of TOS (including the movies) that Kirk cultivated a relationship with on his own, for his own reasons, while he was 100% fully himself and under his own command, which makes her a perfectly unique romantic TOS heroine. Miss Keeler is the one true romance that Jim Kirk ever had, and he never made it past first base with her, because she was not that kind of a girl.
She wasn't a girl at all: she was a truly great lady - arguably one of the greatest ladies of TOS.
Copyright L. Goodwin