"There is evidence that Marianne wrote musical compositions, as there are letters from Wolfgang praising her work, but the voluminous correspondence of her father never mentions any of her compositions, and none have survived" (https://en.wikipedia.org/wiki/Maria_Anna_Mozart)
Now, contrast her case with another contemporary female prodigy, Maria Gaetana Agnesi (https://en.wikipedia.org/wiki/Maria_Gaetana_Agnesi) one can see that not all parents at that time were so ignorant of their daughters' potential.
"When she was fifteen, her father began to regularly gather in his house a circle of the most learned men in Bologna,[9] before whom she read and maintained a series of theses on the most abstruse philosophical questions. Records of these meetings are given in Charles de Brosses' Lettres sur l'Italie and in the Propositiones Philosophicae, which her father had published in 1738 as an account of her final performance, where she defended 190 theses."
Leopold Mozart was no ignoramus (say, like, Gauss' father who tried to stop his son's education so to avoid him being an "egghead"), he could have supported Maria Anne similarly.