Samantha Cesario is referred to as a "late bloomer" in figure skating. She really only broke through last year at 17 and then was derailed by a significant back injury. She is 18, but this is really the very beginning of her career as a top US lady. Not everyone has to hit their peak at 13 years of age..
Cesario chose to do the JGP because she wouldn't get enough damned credit and recognition anywhere else. Senior Bs are not as closely followed and she would only get to compete once. Now, she gets to compete twice at least, maybe 3 times.
I'm so tired of seeing these little kiddies dominate the junior scene. Cesario's maturity and elegance has been a breath of fresh air. Cesario is a "real" junior. She has never competed on the senior level outside of the United States. Your notion that junior skaters should only encompass skaters who are not age eligible for senior is ridiculous, because that only allows 13-15 year old kids to compete. That's ludicrous.