I'm with oder woman on most things, a good structured family and routines produces happy good structured children. I think you should talk to her in a manner that it won't look like you are putting down her parenting.
Unruly children require lots of extra energy, explain to your sister that you would like to see her life a little more simpler and happy as well and through that suggest that she start being a little more disciplined with the kids. Explain to her that while it will be an up hill battle for a while, that the structure and discipline provided to her children will not only make them respect her more in the long run, it will give them more a chance for real success as they start to grow older.
While a book on this issue would be nice, it's not something you give for xmas. Book a lunch date with your sis and let her know how you worry for her, and that you want to see her happy!!!