She posted several photographs, including one of them kissing, to Twitter with the caption: "Don't let y'all being cousins stop you from being in love."
The woman revealed she has had romantic feelings for her first cousin - whose mum is her mum's blood sister - since they were kids.
Writing on Twitter, she said: "Y'all need to get over who I f***. Cousin or not y'all weird asf.
"Can we change the stigma of incest? I shouldn't be limited to who I love because we're related.
"I'm just happy & in love, just so happen to be my cousin. What's the deal?"
The woman, who calls herself Lil Marche online, hit back at hundreds of trolls who targeted her with claims her children would be deformed and God would 'punish her', among others.
"I don't care what anyone says," she posted in response to the negative messages.
"Y'all not going to shame me. I'm happy and in love. No need to be ashamed of it.
"I remember growing up, we had to hide our love from our family. Sleepovers was too lit. Now we grown and we don't gotta hide.
"Blood can't make us any closer but I'm so glad I fell in love with my cousin."