An alternachick is a female version of an alternadude; the concept is the same but the symptoms may vary. Alternachicks like antique shopping, "The Perks of Being a Wallflower" and 'photography'.
The terms are often used derisively and in a condescending manner. Often coupled with ironic remarks.
Did you see Lois's latest Facebook pictures? They're just a bunch of empty chairs with all this filtering crap going on. She's such an alternachick, that one.