I can't remember the name of this Korean Web-novel I once read:
A girl is adopted in her first life by a heroic duke. She worked really hard and had respect for him, but another girl from Korea is reincarnated into her world and the church that used to support the main character is now supporting this new girl. And then she is sacrificed at the church to “save the world”. She comes back to the time she gets to pick which of the three dukes she could get adopted by and this time, to save her life, she picks the villainess duke.
She builds her power and becomes close with the duke and his two sons, but finds out that she has the power to summon devils and use their powers after completing a task for them. And through these devils, she finds out that the church worships an evil god that is trying to kill her.
She also finds out that she is the duke's lost daughter and that the church killed her mother and the reason for that is because, in a past life, she was the younger sister of the now evil god. The pope of the church is in love with that younger sister, as he somehow lived that long? So both the pope and evil god are after her for different reasons.
She ends up contracting strong devils and, through the original god's help, she’s able to defeat them both and lives happily with her family.
The main character has light brown curly hair. (I might be wrong about some details; it's been a minute.)