I dont think 5'7 is that short for a women. Seems like she might have been scrared off but I'll post anyway. Yes you can make them thinner but that requires losing all the muscles mass. It means starving yourself so you body eats itself up. Then your legs will get thinner...as well as your stomach, your chest, your face, everything. Guess what the end result is going to be? Extremely thin upper body, thinner lower body. Still disproportionate..and unhealthy.
I guess there is a healthy way to do it: long distance runner. Have you ever seen a fat or musclar marathon runner? Maybe you could go that route but I hardly find female marathon runners attractive.