Was it ever explained how she knew him?

I always assumed Chris told her about him.

I don´t think so. She never met with Chris after RE2 until you actually see them meet in CV. And even if so... everyone thought he was dead.

Chris broke contact with Claire in August 1998, so she would have known what happened during the mansion incident and that Wesker was a traitor.

Would Claire know how Wesker looked like? I don´t think she recognized him in CVX and she doesn´t even meet him in CV.

Also do we know for sure Chris told Claire about the mansion incident?

The S.T.A.R.S. being suspended probably made head lines.

What other way could she have possibly recognised or even knew his name if Chris hadn't told her.

They have had contact, since she even emails chris earlier in the game. I assume they met up after the epilogue in RE3 and definately before she went off to europe... otherwise why would she stop looking for Chris to go fight umbrella and why would she think an email would work on rockfort island?!

I'm sure she's not that stupid :p

I always thought she was looking for Chris when she was captured. And I don´t remember her recognizing Wesker when she meets him.

But I haven´t played the game in 4 years so yeah... don´t rememeber much.

The impression I remember is that she knows who Wesker is in the sense that he betrayed Chris previously, which suggests she has heard the story from somebody. I'm kinda hazy on it all myself though...