You´re surely right, Prinzheinelgirl, in the question of the pairings decided by Maria Theresa. But it would seem that due to the much mentioned favoritism received by Maria Christina from her mother, or just because of lack of empathy between Mimi and Liesl, Maria Elisabeth -on her own accord- preferred to be with Amalia whenever she could (especially from their teenage years and beyond). I imagine both confiding their early crushes -if to anyone- to each other (Maria Elisabeth in relation to the Prince de Ligne and Maria Amalia, later on, in regards to Prince Zweibrücken), and certainly not to tattle-tale Maria Christina.
I wonder how did Maria Elisabeth (with an "s", being a German name, and not with a "z", as in the English version) react to the knowledge that Prince Zweibrücken was considering her as a bride, in the 1770's, having the Prince been the impossible love (as it turned out) of her seemingly favored sister. Maybe she, aside from the negative political considerations had by her mother, her brother and Kaunitz, was herself not keen to such an offer (on account of her sister´s possible reaction). But then again, we need to have more sources at hand on the subject, to be anything more than speculative.
What did you mean (Prinzheinelgirl) when you said "If you see Maria Elisabeth´s paintings, she was good at it" ?? I imagine you refer to the art produced by her, and not to Elisabeth´s portraits done by others (which was the first thing that came to my mind on reading your phrase). I understand Amalia was also very gifted in this, and that there is a very good painting of a Saint (is it Saint Anthony?) attributed to her and kept in a private collection. However, I am inclined to think that many of these paintings were very much "retouched" by the court artists and professors, who wanted to enhance and flatter their pupils´skills (and therefore their own educational abilities !!). Once more, we need more studies on the subject.
I coincide completely with you, in relation to the unfounded belief that Marie-Antoinette was Franz Stephen´s favorite. His much publicized decision to stop the carriage (was it so?) to embrace his youngest daughter one last time, seems to have been a much romanticized exaggeration, the authors (and chroniclers) wanting to match his soon sudden death with this daughter´s tragical end. There doesn´t seem to exist any more evidence as to this pretended favoritism, beyond the natural weakness a parent may feel for cute younger children...