Akkadian bilingualism would have become common in the elite, and one can see evidence of this at the highest level, since Sargon's daughter Enheduanna is supposed to have composed two cycles of Sumerian hymns, and the most famous (to Innanna) has been found in some fifty copies.
This participation by women, especially princesses and priestesses, in Sumerian literature was not uncommon. They wrote funeral hymns, letters and especially love songs.
Thy city lifts its hand like a cripple, O my lord Shu-Sin
It lies at they feet like a lion-cub, O son of Shulgi,
O my god, the wine-maid has sweet wine to give,
Like her date-wine sweet is her vulva, sweet is her wine.....
(in background here, Sargon and his daughter were not Sumerian, they were Akkadian - and their language was not at all closely related, although they adopted the Sumerian cuneiform writing system for their own language and kept Sumerian culture alive)
Does anybody have any cunnilingus reference that pre-date this?