What is remarkable about Mr. Jagger's housekeeper?

Molly's strong wrists are seen as incredible. Mr. Jaggers take careful note to make us, as well as Pip, aware of her strength.

Pip later realises that he has seen many of Molly's characteristics before, similar to someone who's dear to him, Estella, and plots in his head that they must somehow be related also leading him to question Wemmick about Molly's past.