It depends really. Right now I've been playing up that she's really just "shellshocked" over seeing him behave this way and once that fades, curiosity will set in. What happened to cause him to change, is there a weakness that can be exploited, etc? These are things she'll have to keep an eye on while struggling with the knowledge she carries.

If there's anyone she'd tell, it'd be one of the "older" ninjas depending on who's there. Itachi, if they can build up to it, might be a preference compared to Minato who is their teacher. It just really depends on who gets under her skin enough to get her to fess up.

There's always Naruto and Shino that she can talk to as well. Likely Shino over Naruto since he has his family here to spend time with, Sakura would feel guilty over taking him away from that whereas Shino could use some time in the spotlight.