She was born Elizabeth Christina von Braunschweig-Wolfenbüttel, Protestant in 1691 and reluctantly converted to Catholicisim. She bore four children, but only two two survived, Maria Anna and Maria Theresia. There is another Elizabeth Christina von Braunschweig-Wolfenbüttel, born in 1715, in this album. Her Wikipedia article is here.
She was born to the Welf family branch in Braunschweig-Wolfenbüttel; the family’s Hanover branch is better known and comes down to us today through their branch in Hanover and their UK branch known as the ruling House of Windsor. The current Prince of Hanover, Ernst August, is married to Princess Caroline of Monaco, her third marriage.

1730 Holy Roman Emperor Karl VI, Empress Elisabeth Christine, Archduchesses (l.-r.) Maria Amalia, Maria Theresia and Maria Anna by Martin van Meytens (location unknown to gogm)

Elisabeth Christine of Braunschweig-Wolfenbuettel Empress of Austria by ? (location unknown to gogm)
