Hera in Homer's Iliad is the Queen of the gods, and the wife of her brother Zeus who is the King of the Gods. She is the goddess of marriage and childbirth, and thus opposes the Trojans because, inter alia, the Trojan side of the war was supporting Paris and Helen, who were involved in an adulterous relationship based on Paris' having abducted Helen, wife of Menelaus. A further issue here is that Zeus is a serial philanderer and Helen is one of his illegitimate children by a mortal woman Leda whom he seduced by taking the form of a swan.
Hera's most admirable characteristics are that she is strong-willed and intelligent, able to devise cunning stratagems to outwit her husband. Although some people might see her feuds with her husband as a negative element in her character, given that he raped her to force her into marriage and later tortured her when she led a rebellion against him, as well as routinely committing adultery with both mortal and immortal men and women, I see her struggles against him as evidence of strength of character.
While Hera can be petty and vindictive in her treatment of other women who attract Zeus' roving eye, she is a strong supporter of legitimate marriage and of the Greek cause. Hera's scheme to seduce Zeus as a way to distract him is quite clever, and she shows herself wise in the counsel and aid she gives to Achilles and in her alliances with Athena and Aphrodite.
On the negative side, her interference serves to prolong the Trojan was and she shows herself as quite vindictive and duplicitous.