there's multiple things i can think of and they all are kind of interconnected!

loss of control was one of her earliest fears and it stems from the accident with her brother. nymeia's blessing is responsible for saving her life but with it comes great power that if she doesn't take reins of can hurt other people. not even the best healers could heal her brother's burns and that really stuck with her and influenced the kind of person she grew to be. she's getting better about it but the more she discovers about her abilities the more that control wanes.

loss of self in the sense that being on top of that pedestal everyone holds her up on because of her strength and blessings. the doubts that eat her inside about who she is and whether the love she receives is true to who she is or if it is the face she wears in the name of duty.

and lastly it would be not doing enough by others, which connected to the previous two because she learned control and performs her duties for the sake of others and protecting them. her heart is rooted in service and she would do all that she can for those who seek her help or guidance.