Oh, and, ummm...
The reason I point out the age thing.
Just a thought. *whistle innocently*
Thoughts on Sacha's view: She's not really gumdrops and rainbows so much as she is willing to make a snarky comment about anything and everything. And in believing the best possible outcome of a scenario is certain to come true(which is not unfounded as it happens a disproportionate amount of the time with her). She understands when things are bad or dumb, but she doesn't like to ruin anyone's day, so she tries to cheer them up. She always has a smile like she knows something you don't and would love to share it with you if you'd only ask. She's certainly eager about life but less childish and more just not thinking things through - or not caring(maybe that's what Sacha means, though). She is, however, rather impatient, which Sacha might be upset about. She's supposed to be charming as much as she is beautiful, and it's not exactly clear who she's attracted to(which is mostly for reasons of allowing more angst) since she only ever makes jokes about it.
Also she doesn't know about paladins yet, other than stories, and given what's known about them, and her, it's seemingly obvious she would make a terrible one, for all that she denies it.
Oh yes, and did I mention that she constantly does stuff that sane people would probably be too scared/smart to, typically involved things that end up risking her life?
EDIT: Sorry if I'm contradicting you or anything, but seeing other people's perspectives on her personality allows me to try and describe it better. I'll try and adjust her personality description to better show what I said but it might be a while.