When my 2.1 years old daughter was smaller, I trained her to sleep by herself.
However, these few months, if she's not too sleepy when I leave alone in the room her after evening milk, she would cry out loud and able to make herself vomit so that she can be rescued. After cleaning up, and I would left her in the room alone again to let her sleep, she would do the same thing gain (vomit) until probably she has nothing in her tummy then eventually sleep after crying for sometime.
Am I doing it right? Should I keep leaving her crying out loud and vomit? Please help, I'm not sure what is the best way.