Possible Answers
* A statue: Statues are often depicted as mighty women, and they cannot speak, thus having silent lips.
* A portrait: A portrait could be of a mighty woman, but the image is silent.
* A memory: A memory can be powerful and evoke strong emotions, but it doesn't speak.
* The ocean: The ocean is often personified as a powerful feminine force, and its waves crash silently against the shore.
* A grieving mother: This answer is more abstract, but a mother's grief can be powerful and silent.
Let me know if you have any more clues or context, and I can try to refine my answer!