Sounds like your daughter is a great sleeper, congratulations! As you know, all babies (and parents) are different, so what works for one might not work for another. That said, my little girl fell asleep well in my arms at that age, but not on her own. We did a combination approach that was one of several options outlined in "Sleeping through the night" by Joni Mindell. I would get her nearly asleep in my arms (eyelids drooping or closed but not yet fully asleep) and put her down. Of course, she'd come fully awake and start crying immediately, but I'd leave her for 5 minutes before I picked her up again and did the same. Eventually I'd leave for longer periods (10 min, 15 min) and she started getting herself to sleep before I had to come back and repeat. When she started staying asleep, I started putting her down more and more awake. This gradual approach takes longer--think two or three weeks, but it was easier on us both and she became a great sleeper and self-soother. Be ready for bumps in the road later--as she hits cognitive development milestones, changes in eating habits, teething, colds, etc., her sleeping may experience set backs. Don't get discouraged, just use the same methods you found worked before to "train" her yet again. Our baby is 12 mos now and is a great sleeper, though she went back and forth from 6-11 months. Good luck!
Another thought--don't listen to people who say one or another method is wrong. You are the expert when it comes to your child and family, and only you can say what is right or wrong for you and your family. Trust yourself, and do what works best for you and your baby.
J.