Hello and thanks for your question and for buying my book The Camelid Companion! You didn't mention how old your cria is so I will assume that because you use the word cria but are training her that she is in the 4-8 month old range. If this is the case I think you can simply wait and see what a bit of age does. Many young animals, especially if they are big for their age are gangly and uncoordinated just like human teenagers and will grow out of it. In the meantime since you do have my book I will refer you to several different aspects of handling that may impact her behavior and that are described in more detail in my book.
1. You could try a body wrap. This would draw attention to her balance and might help her find a new and more attractive way of standing. (Chapter 10) Since the book was published I have begun using a body wrap alternative a "neck wrap" that is a bit easier to get on and off and still makes a huge positive impact on balance. You can find out more about the neck wrap on the Camelidynamics Guild Forum http://www.camelidynamicsguild.com/guildForum/index.phpsearch neck wrap or read about it on my website here: http://www.camelidynamics.com/home/cam/page_606/the_neck_wrap.html
2. Make sure that you are not inadvertently causing your animal to have trouble with the balance in her back end by being heavier than you need to be when leading. Use a lead that is at least 7 feet long and allow the animal to have some distance from you as you lead even if this means that she walks more slowly that you consider ideal. (Chapters 6 and 9 will give you much more information on leading techniques that will help) Often animals learn to use the handler for balance because the handler offer steady pressure on the lead in an effort to get the animal to walk faster. Look at the hook on your lead where it attaches to the halter it should be dangling freely as you lead, otherwise you are pulling and this will definitely affect the rear end balance.
Good luck and happy handling!