The British Envoy to Naples, Sir John Gray, considered Charles and Maria Amalia "the ugliest couple in the world" and Charles de Brosses wrote in 1739, when she would have been about 15 that "This worthy Princess has a malicious air, with her bullet nose, her crayfish features and magpie voice. 'Tis said she was pretty when she arrived from Saxony, but she has recently had smallpox. She is still quite young, and has not yet grown up. (At the time I wrote this she was a month or five weeks with child, which happened to her before any sign was apparent)."
Maria Amalia was on bad terms with Louise-Elizabeth of France when she was about to go to Spain on the death of Ferdinand VI, as Charles had been negotiating the marriage of his and Maria Amalia's daughter with Maria Theresa's son, the future Emperor Joseph II. However, Louise-Elizabeth nipped in and arranged with the Austrian ambassador in Paris to substitute her eldest daughter Isabel instead. Maria Amalia was so furious at this French perfidy she changed her travel plans, which had included paying a visit to Bayonne to see her sister Maria Josepha, the Dauphine of France, and travelled by sea to Spain, although she was a bad sailor. So while both daughters-in-law detested Isabel Farnese, they didn't make common cause against her.