Shakespeare does an excellent job of characterizing Helena as a very young, very beautiful, very emotionally needy woman.
We learn about Helena's beauty when we meet her for the first time in the very first scene of the play. After Hermia has left stage, Helena delivers a soliloquy to bear her heart about how Demetrius is tormenting her by his rejection of her. The first thing Helena points out in this soliloquy is that all throughout Athens she is recognized to be as beautiful as Hermia, which is one reason why Demetrius has no real reason to reject her, as we see in her line, "Through Athens I am thought as fair as she" (I.i.232). Helena's beauty contributes significantly to Shakespeare's theme that love is foolish and irrational, as we see when Helena points out that love is based on one's imagination rather than any objective reality, such as beauty, as we see in her lines, "Love looks not with the eyes, but with the mind; / And therefore is wing'd Cupid painted blind" (239-240).
We also learn through Shakespeare's characterization of Helena that she actually may be more beautiful than Hermia because she is taller. We learn about Helena's height when we see a few "short jokes" being relayed in Act 3, Scene 2. After Helena finds herself being pursued by both Lysander and Demetrius she believes it is a joke being played on her and that Hermia is in on the joke; hence, she refers to Hermia as a liar and false friend and also insults her height, as we see in her line, "Fie, fie! you counterfeit, you puppet you!" (III.ii.298). While the term "puppet" is a little vague, we see in Hermia's response that she has indeed interpreted Helena's remark to refer to Hermia's own short stature, as we see in Hermia's lines:
'Puppet!' why so? Ay, that way goes the game.
Now I perceive that she hath made compare
Between our statures; she hath urged her height;
And with her ... tall personage,
... she hath prevail'd with him. (III.ii.299-302)
A final thing we learn about Helena from Shakespeare's characterization of her is that she is a very typical emotionally needy woman. Demetrius sadly turns her into an emotionally needy woman when after proposing to her, he decides to pursue Hermia instead. Demetrius's rejection has made Helena do what most women would do in her situation--pursue Demetrius to try and win him back. As Helena points out in the opening scene through her conversation with Hermia, the more she shows Demetrius love, the more he hates her, as we see in her line, "The more I love, the more he hateth me" (I.i.203). We also see how desperate and needy she is when she follows him into the woods, even though she knows he is going in pursuit of Hermia. Shakespeare uses her acts of desperation and neediness to portray just how foolish people can act when they are in love.