Barbara, Treadwell 1986-2001,” as its title suggests, is a memorial show. Its subject is a girl Andrea Modica met by chance in 1986, when she photographed the pudgy seven-year-old on a porch in rural Treadwell, New York. Barbara died 15 years later of complications from childhood-onset diabetes, ending a rich, complex, and intensely emotional collaboration. From the beginning, Barbara was a striking presence: a Rubenesque urchin, sad and sweet and a little sly, who responded to Modica’s rapt attention like a flower that turns toward the sun. The photos they made together are closer to Julia Margaret Cameron’s allegorical fictions than some documentary freeze-frame, and Barbara emerges as a vaguely mythic, tragic figure, especially in the remarkable sequence of pictures made just before her death. At 22, she had become so buried in her flesh that she looked like an enormous baby. Modica observes her close up but in tender soft focus, so the sleeping Barbara appears ready to drift away—to dissolve, finally, into memory.