Lily's pretty much summed up in the observations of other characters.
"She ain't blonde. She's got kinda light brown hair. Wears little spectacles like a schoolmarm or something. An' she looks about Fiona's age…."
"Fiona's what? 19? 18?" Wash wrinkled his brow.
"She's 19." Storm said. "Quick, eyes, height, whatever. I want to go to sleep."
"Lessee, don' rush me. This is important stuff. "I think her hair's kinda long, she had it piled on top of her head an' it was comin' out in little frizzies. Has light gray eyes. Looks like she's been on the road some, an' her face is a little red from the sun. She's about as tall as…." Luis drew himself up to his diminutive height and gestured a couple of inches over his head. "This. About like Tommy. She's a little skinny, but she carried them bags into the house before I got to her, so she must be strong enough. She's sweet lookin'. Got a soft voice, too. I liked that."
His gaze traveled discretely up her arm as her hand slid off the pot handle and took inventory on their way to her face. Slim, but, as Luis had correctly commented, strong enough. Her arms below her rolled-up shirtsleeves were a little sun-browned from her travels. Her neat apron hung from a trim waist, and her slight build swelled girlishly beneath her calico bodice. Open, readable face, her cheeks flushed with warmth and self-consciousness, and her clear grey eyes, hiding behind a pair of frumpy little spectacles, were honest and guileless. Her light brown hair was piled on top of her head in roll, wisps escaping in slightly unruly tendrils. She wasn't the fiery beauty that Fiona was, but she was quietly pretty, and Saint found her gentle face appealing. She wasn't the sort of girl he was used to dealing with in town,that was for sure.