In the vast international anthology of stories about vulnerable young people trying to make sense of bewildering, hand-to-mouth circumstances, Rosie, a spare and gritty Belgian entry, is notable for the unusual, unforced empathy with which writer-director Patrice Toye presents her troubled adolescent heroine. Rosie is a child in sore need of the mother who wants to be called ''sister'' (Sara de Roo) -- herself harboring ugly secrets -- and she's also a young woman who uses fantasy to fill in all the vacant or overwhelming spaces in her untethered existence. Holding together the considerable miserableness of this patchwork family, Aranka Coppens, as the title character, is natural and heartbreaking as a girl made to grow up too fast.