I know the meaning. I know it shows that she has long legs. I think the author adds one image to the list. He already used other names of animals: Faralona- salamontes- zancuda
By using long-legged girl you lose the image.

Yes, you can call someone a long shank or a longshanked girl, but it is an antiquated and rather unusual term.A "shank" refers to the leg or shin. Therefore, "longshanked" simply means having long legs, and is a descriptive synonym for being "leggy" or "tall".However, because it sounds old-fashioned and slightly awkward, calling a girl a "long shank" directly to her face might come off as strange, comical, or potentially rude depending on the tone. If you are describing someone's height or long legs in modern conversation, words like tall, leggy, or long-legged are much more common and natural alternatives

longshanks keeps the image. the bird is long-legged

the long-legged girl?

faralona- salamontes- zancuda