I think hint would work well for getting some of what auYuna's holding in off her chest while not telling Yuna to much. :)

As for the Big Sis thing, well, auYuna is like 4 years older... she's got stories. Some embarrassing and after they work past the I'm myself I just share a face with this person I'd love for them to be close >.< Sisters are fun. And auYuna is at the point where she is like, I've been through so much I'm gonna leap to the defense off and back whatever is up with Yuna lol. Summoners gotta stick together :p