Helena and Hermia were good friends, until Demetrius fell out of love with Helena and into love with Hermia. At the beginning of the play, therefore, Helena is jealous of her friend, wondering what Hermia has to attract men that she doesn't. Helena sensibly concludes that love sees with the mind, not with the eyes. In other words, she realizes that while Hermia is pretty, basically, Hermia is not much different from her. She and Hermia are both attractive. The problem is that love is irrational.
Helena wishes Hermia no harm through most of the play. In fact, she wouldn't mind seeing Hermia achieve her desire of marrying Lysander, as that would leave Demetrius free for her. Near the end of the play, however, when she thinks that both Lysander and Demetrius are making fun of her by pretending to be in love with her, she gets angry at Hermia, because she thinks Hermia is part of the cruel joke. Hermia, in turn, is angry at Helena because she thinks Helena deliberately stole Lysander from her. By the end of the play, however, both women are paired with the right man and back to being friends again.
Basically, Helena shows herself to be a sensible, clear-thinking woman who is capable of strong friendship with Hermia—until love's lunacy interferes and turns her into another kind of person.