Removing compulsion without destroying the victim's mind is a subtle and tricky operation. Semirhage would probably be among the best to try it. If SH somehow removed the compulsion by simply nullifying the source (assuming he can do that), it may have left Elza useless for anything else.

This doesn't prove SH broke Cadsuane's wards as we don't know that he can affect existing weaves, but it does keep the possibility open.


EDIT: As Datakim's post below has reminded me, BS has already pretty much implied that Elza penetrated the wards after being given knowledge of the necessary weaves to do so.