well, you can either humor her with girly weights, or convince her to 'trust you' -- you don't want her to look like a man & she couldn't lift her way into that look w/o chemical 'assistance'...
the lithe lady i train most is addicted to lifting and two years in she still looks rather more like a tennis player than any other body type (when she started she looked like a soft but skinny tennis player from the 70s and now she's built like almost any gal [excluding the williams sisters!] playing tennis these days -- think sharapova's bod!)
she's gotten there doing basically effort's "where to start" Option B program (
http://www.sosuave.net/forum/showthread.php?t=125444) and never eating quite enough protein. oh well! she's a fiend for poultry, salads & oatmeal, and has been slow to embrace eggs & beef.