Ploomette had a lot of resemblance with princess Cadance!

"The more I see Ploomette and the more I doubt she can be Cadance sister!

they have a lot in common : the body color, some of her hair colors, she had an heart for cutie mark (like the Apples family have all apple related cutie mark) and she’s a Pegasus like Cadance before she became an Alicorn

Well, we haven’t seen Cadance family (no even at her wedding!) and since she’s the niece of Celestia (and Luna ?), I think she was adopted into the royal family maybe her parents are dead and she doesn’t know she have a young sister."

Cadance & Ploomette © Hasbro