Board Thread:Questions and Answers/@comment-35176732-20190720021441/@comment-32147440-20190720024335

Remember that Nya always wanted to contribute to the team, whether it be as Samurai X or the Water Ninja. While she did fear failure and weakness, she overcame that and in realizing its okay to fail. In the process, she acted as the Water Ninja and found her place on the team.

So now that she's found that place, not only would it make sense she'd fear losing it, but this even ties into her previous fear in a way since she might find herself feeling weak again if she loses being the Water Ninja.