I Became the Black Swan Mother of the White Swan Princess

The transmigration that happened to others happened to me, too. I’m pretty sure I’m now a supporting character… but exactly which novel is this?
When I opened my eyes, I was a widow with stepdaughters my own age, and not only that, I turned into a black swan every night due to a dark curse! Holding back my tears, I decided to take charge of my fate…wait, why should I? Why So Serious?
A duchess during the day, a queen of the lake during the night – I have the best luck to be able to leisurely float around! Life should be lived unplanned! When I had just about decided to live my life like this, a white baby swan, one that was not in my no-plan life plan, came to me.
“Mommy, are you really my mommy?”
What, you were a person? And even the youngest sibling of the tyrant emperor?
“I’m not your mother! Can’t you tell by the different colors of our feathers?”
I’m a black swan, you’re a white swan! But why is she so crazy cute. Can our mother-daughter love endure the obsession and persecution of this child’s seven brothers, including the tyrant emperors?