It's Elisabeth Wilhelmine. The picture was painted by Johann Baptist Lampi in 1785.
Elisabeth was brought to Vienna in 1782. She was educated in a monastery founded by Empress Amalie Wilhelmine. In 1788 Archduke Maximilian Franz, the youngest son of Maria Theresia, made the marriage ceremony for Elisabeth and Franz.
Emperor Joseph II. loved Elisabeth a lot. When he was told that Elisabeth had died after she had given birth to her daughter Louise Elisabeth Franziska, he was devastated. Joseph, who was seriously ill, died two days after his beloved Elisabeth.