For the purposes of this discussion it doesn't matter whether Lelaine is Black or not but I believe it to be Lelaine.  She said something to the effect that she pressed Faolaine very hard, that kinda implies to me that she is not averse to use extreme force.  Faolaine is blue and so was Sheriam, so I believe Lelaine is "pressing" Sheriam for information.  I happen to believe that Lelaine is Black but my belief is not certainty

I'm all for giving Lelaine to Romanda on genenral principals, black or not. :D

 

On topic, however, I don't *want* to think that Sheriam is a Dark Friend, but I find it had to work out why she didn't defend herself / hasn't done something about the one "pressing" her for information; she is an Aes Sedai and not a weak one at that.