what does "Birthright" symbolize?

I think her femenine sexuality becomes not some thing that a man exacts from her but a birthright. As the storm climaxes, so does their affair.

"They did not heed the crashing torrents, and the roar of the elements made her laugh as she lay in his arms. Her firm, elastic flesh that was knowing for the first time its birthright, was like a creamy lily"