To be fair, Sybilla is considered one of the worse princesses on DMM. Olivie is actually a really good go-to choice. Don't let that low health pool distract you, she has the highest defense, resistance and attack of all the princesses and will survive most things.

Personally i'd CR/SU the main Sybilla, but that's also a lot due to not wanting to have 2 of the same unit. People will whine when i say that i would do the same with 2x Nanaly, but they can go screw themselves :P