Valaena is barely more suitable than say, Laena Velaryon in that she can keep it in her pants rather than just assuming "everything will work out", and she's still a fan girl even having read the history.
I guess one of the qualifying pre-requisites would be having too much tying them down to ever contemplate abusing the position, which she (Valaena) certainly does, but have you ever considered everything she (Ceria) does is motivated by wanting roots to lay down and not having someone holding an axe above her head every day, threatening to uproot her?
She's wary and cautious, not ungrateful or disloyal. Hell, she risked life and limb for random strangers on a journey of self discovery out of loyalty to her friends, because they were kind to her.
Have you considered you just don't understand her character at all?
Perhaps I'm a complete idiot who forgot something huge, but AFAIK despite being a badass with trust issues and a hidden vulnerable side (
TM) Ceria doesn't seem especially attached to the Empire or us. She's attached to her friends and companions (yay Misfits!) and probably grateful to us, but that isn't the same thing as loyal.
So far I got the impression that she served us because we promised a place of safety, without stigma, and where she could do good. Indeed she fights with our baby PCs not just because if the amazing pay and power (buying gratefulness is a great strategy when you're rich like us!) but because she's a good person who values human lives.
All of these are good things... But if her friends quit or if she thought our Empire wasn't good, she would leave. Basically she feels fundamentally driven by ideals and friends, and we don't really have a firm grip on the friends (and our Good Vs Evil meter is just
weird).
This is why I still don't consider her dependable.
She isn't pragmatic and obviously open to incentives like Malarys, but she isn't a true believer in our Empire either.
Meanwhile Valaena is stupidly grateful and deeply tied to us through loyalty+family+ambition+personal rapport, her power-leveling is going very well, and more importantly giving her a Dragon was a huge symbol given to the world : old allies should return, and they won't be forgotten !
It also got us her dad (who has been super useful in the 7K) and didn't cost us much, as she came with her own egg.