In Little Women, why do you think Alcott kills Beth and how does that fit with her feminist agenda?

I think one of the main reasons that Alcott kills off Beth's character is that she was basing the March family on her own family, and her sister in real life, Beth, died young too.  Alcott seems to honor her, especially, with Little Women because she is the only sister whose name was not altered for the novel: Anna Alcott became Meg, Louisa (or Lou or Louie as she was called by friends), Beth remained Beth, and May became Amy.  

Further, Beth's whole life has revolved around her family: taking care of them, taking care of the house, tending their pets, and so forth.  She is painfully shy, far too painful to ever go out and get married.  She doesn't have any source of income; if she cannot go to school because she's so shy, then she won't be able to procure real employment either.  Once all of her sisters move out (which they all do), and her parents pass on (which they will do), what can Beth do?  Where will she go?  If she moves in with a sister, in need of support, she might fret that she's become a burden, and no one would wish pain for Beth.  Beyond this, Beth is an innocent, and to grow up and grow old might mean losing that innocence, and we wouldn't want that for her either.

In addition to the problem of her future, Beth has already fulfilled the goal that the book seems to claim is the whole purpose of life.  She has lived selflessly and achieved a goodness that is unmatched by any other character in the book.  Her gentleness and tranquility make her seem like an angel on earth, and this makes it equally as difficult to imagine a future for her.  

I don't think Beth's death necessarily fulfills some kind of feminist agenda.  Some might say, I suppose, that Beth has effaced herself to the point that she has no self left and that she must die as a result, but I don't think that is fair or accurate.  Beth hasn't given herself up by staying at home; on the contrary, she's found herself by staying at home, and this is partially why she has to die, I think.  She's only feels at home when she's at home, and so the only place for her to go next is her heavenly home.