There's no proof that Verin even knows Compulsion, and there are strong hints that no Aes Sedai knows it. This was confirmed when Moghedien showed off her skills against Liandrin, who also thought she knew the weave. Verin's weave, at best, probably steered them to serving Rand. She hid the weave expertly and said only the best delving would find it.

It's very unlikely that Moridin delved a Black Sister to see if she was tainted by some sort of mind weave. Elza also doesn't act strangely, so he wouldn't have any suspicion to do so. Not only that, but Shadar Haran or Moridin would both have to have great skill to deduce the function of some sort of weave of saidar hidden well in Elza's mind.

It's much more likely that Moridin used his own Compulsion on Elza when he arrived there to get her to perform certain duties to ensure Semirhage's success. Thereafter, he had her tell Semirhage that she had a weave on her, which she should remove to remove any limitations the weave would have and make her useful.