Is there a legend or an explanation for the symbol of a swan with a woman's head?

Question

This was found in a grave of a knight in Romania and I am wondering what the symbol of the swan with a woman's head could symbolize.

The grave has a templar cross at the feet of the knight, the star of David at the head and on the top the tree of life, a 12 pointed star with a solar symbol in middle.

Top part of the grave:

This is the grave with the knight in it. The historians think it is the son of Basarab I, the knight is known under the name of the black knight of Wallachia. Wallachia was founded as a principality in the early 14th century by Basarab I, after a rebellion against Charles I of Hungary, although the first mention of the territory of Wallachia west of the river Olt dates to a charter given to the voivode Seneslau in 1246 by Béla IV of Hungary. In 1859, Wallachia united with Moldavia to form the United Principalities, which adopted the name Romania in 1866 and officially became the Kingdom of Romania in 1881.

Carbon 14 tests and DNA tests "tell" the man buried at Curtea de Arges had died between the years 1340-1350. That his mother had german or nord-indian origins, not cumans how some historians tend to say.

Answer 1

According to a post on Total War Center:

Inside the portal to a closed area with email, there is a female swan head cast in silver (the figure may represent the folk figure named Melusine, feminine spirit of fresh waters in sacred springs and rivers).

According to Romanian Coins:

The man represented on the buckle is considered to be Louis the Great, king of Hungary (1342 - 1382) and of Poland (1370 - 1382). The woman is considered to be Elizabeth of Bosnia Kotromanic, the second wife of king Louis of Hungary, daughter of Stephen II, Ban of Bosnia, and descendand from a Polish king. The swan with human head is considered to be the heraldic sign of the queen.

and according to Wikimedia:

Swans are used in heraldry and can represent loyalty and grace among other things.