Her jealousy showed up a bit in when Edmund was teaching Mary to ride. Again it showed when she sighed at the window as Edmund moved off to admire Mary at the piano rather than go star gazing as he'd just suggested.

When Edmund and Mary read lines in front of Fanny, the hints are too strong I think to be imputed to disapproval of the idea of acting.
ch. 18
She could not equal them in their warmth. Her spirits sank under the glow of theirs,
...She believed herself to feel too much of it in the aggregate for honesty or safety in particulars...
agitated by the increasing spirit of Edmund’s manner, had once closed the page and turned away exactly as he wanted help...
their performance would, indeed, have such nature and feeling in it as must ensure their credit, and make it a very suffering exhibition to herself.