I see Helena as a prisoner of her passion for Demetrius, which, to be fair, he is responsible for arousing by his previous amorous attentions to her. She is a woman seduced, (metaphorically), and then abandoned, and she has not recovered. I do not see her infatuation with a former lover, or her treatment of Hermia as a lack of empathy. The four lovers are pretty much interchangeable and are illustrations of Shakespeare's attitude about a certain kind of romantic passion that blurs the mind, wreaks havoc with any kind of personal balance, and makes us pawns in a romantic chess game over which we have no control.
The quote that best describes Helena's state is spoken by her in her monologue at the end of Act I,scene1:
"Love looks not with the eyes but with the mind;
And therefore is winged Cupid painted blind.
Nor hath Love's mind of any judgement taste.
Wings, and no eyes, figure unheedy haste.
And therefore is Love said to be a child
Because in choice he is so oft beguiled."
Although the plot concerning the two pairs of young lovers in A Midsummer Night's Dream by William Shakespeare is highly entertaining and drives our introduction to the magical world of the forest, the young lovers themselves are not actually among the most interesting or fully developed of Shakespeare's characters. Motivated by her infatuation with Demetrius, she is willing to betray her childhood friend Hermia with no qualms at all, and acts mainly to advance her own personal ends, having little empathy or understanding for the other characters of the play. In the comic cat-fight between Hermia and Helena, we find out that one of her distinguishing characteristics is that she is tall and Hermia short. Her pathetic chasing after Demetrius despite his fickleness suggests a lack of self-respect.
One quotation that illustrates Helena's character, emphasizing her tendency to self-pity, comes from Act II Scene 2:
Wherefore was I to this keen mockery born?
When at your hands did I deserve this scorn?...