She emails Leon.

I always found it to be a pretty stupid idea of capcom's to reveal to Claire first that Wesker was still alive, she doesn't even know who he is.

I am sure that at some point Chris was talking about his asshole boss to his sister before.

Possibly, but since during the time of CVX she hasn't heard from Chris since before RE2, I doubt she knew Chris's asshole boss tried to kill him, or was dead and came back to life.

Also, if your brother told you his boss was an asshole, would you really be able to tell if some random person you just meet was your bro's asshole boss? Even if you did see a picture a few months earlier, I doubt you'd remember the face. Even if Chris did go out of his way to describe him (which he probably wouldn't in passing conversation at the Redfield home), and told Claire that he looked evil like the T-1000 from T2, wore sunny's at night, always wore black, and even showed Claire a photo of him Chris kept in his wallet, just in a passing conversation, Claire probably wouldn't recognize who he was when she saw him at Rockfort.

So I do think it's a bit weird that Wesker was revealed to Claire first.

She checked Wesker's desk 50 times in RE2, duh :P

I always thought if she had the information to break into Umbrella's Paris HQ she could have easily done some background research as to why Chris went missing; or maybe before the Mansion Incident and subsequent events kicked off he showed her a picture of the S.T.A.R.S. group or something.

She does see the S.T.A.R.S. photo in RE2, and Wesker is clearly in it.

Other than that, I doubt they've met before CV.

I agree.

I always thought that that she found out between RE2 and CV