I tried to find biographical information about this sumptuously dressed person. It turns out the word "monialis" in Latin means nun. So this Sister could be a noblewoman named Anna Josepha. Running the caption at the lower right through Google produces something like "Anna Josepha Sister professing (at) St. Augustin Monestary, daughter (of) Count Joseph Maria Arconati, worldly (name) Livia."
From Wikimedia.