She may seem weaker than Lanfear because she is hiding her strength, in order to make the other Forsaken think Lanfear is dead or to avoid explaining the circumstances in which she is now being punished as Cyndane.

In this case, which I thought up quite some time ago, she isn't weaker because of an outside agency or her new body, but because she wants to appear as a completely different person. Perhaps this was a way for her to learn humility in order to prove herself trustworthy to the Dark One and enable her mindtrap to be removed?