Jo March isn't a tomboy, she's Transsexual
Amy: "Don't Jo. It's so boyish!"
Jo: "That's why I do it."
Jo: "It's bad enough to be a girl, anyway, when I like boy's games and work and manners! I can't get over my disappointment in not being a boy."
Beth: "Poor Jo! It's too bad, but it can't be helped. So you must try to be contented with making your name boyish, and playing brother to us girls."
[Jo had] the uncomfortable appearance of a girl who was rapidly shooting up into a woman and didn't like it.
Jo: "I'm the man of the family now Papa is away."
Jo: "I'll try and be what he loves to call me, 'a little woman' and not be rough and wild, but do my duty here instead of wanting to be somewhere else."
No gentlemen were admitted, so Jo played male parts to her heart's content.
...Jo, who didn't care much for girls or girlish gossip, stood about, with her back carefully against the wall, and felt as much out of place as a colt in a flower garden. Half a dozen jovial lads were talking about skates in another part of the room, and she longed to go and join them...
Laurie: "There isn't anyone I'd like to see. Boys make such a row, and my head is weak."
Jo: "Isn't there some nice girl who'd read and amuse you? Girls are quiet and like to play nurse." (note how she almost seems to be responding to him as a boy, and talking about girls as "other")
Jo: "I'm a businessman - girl, I mean."
[Jo] seemed to understand the boy almost as well as if she had been one herself.
Laurie: John is going home with you, as I can't.
Jo: No need of that. I am not a young lady, and it's only a step.
Jo felt as if during that fortnight her sister had grown up amazingly, and was drifting away from her into a world where she could not follow. (world of womanhood)
In the musical version, Jo March is the Slayer.
Aunt March: You spend all your time writing senseless stories, constantly trying to save the world, when you can't even save yourself!
Jo: I don't need saving.
Aunt March: You'll marry! All girls marry.
Jo: I'm not all girls.