What is key to understand in order to answer this question is the way in which the symbol of the wild duck in the play is such an important symbol for so many different characters. For example, Hedvig can be considered to be the wild duck in the way that she is completely friendless and alone, left stranded in a place without any of her original family and that is not her own home.
Hedvig's final suicide further elucidates this link between her character and the symbol of the wild duck when both Hedvig and the wild duck become objects that other characters are willing to sacrifice. After all, when Hialmar has abandoned Hedvig, Gregers forces her to dispose of the duck, which is her most valuable belonging, in order to show the love that she has for her father. Hedvig ostensibly enters the garret in order to sacrifice and kill the duck, but ends up only killing herself. In a play that is so much about depicting Hedvig as some kind of innocent in the play who is not meant for the complex world of machinations that she finds herself in, her suicide is, in one sense, a logical response to the way in which other characters view and treat her.