John Marshall Clemens was a son of Pamelia Goggin and Samuel Clemens. I checked the names of Pamelia's children from both marriages and I find no Amanda. John Marshall Clemens has no daughters named Amanda. I have no record of siblings for Pamelia's husband Samuel Clemens.

Samuel L. Clemens (Mark Twain) had some cousins of varying degrees that were named Amanda, but none of the ones I know about had the Clemens surname as they were all related to him through his grandmother Pamelia Goggin Clemens Hancock.

I see from your post that you are saying the lady in question was named Amanda Clemens 'something'. In a situation such as this the maiden name is pretty vital. Let me know if you locate it and I will check again.