The father of Historia's daughter is Levi.
Hair texture is where hereditary traits show up strongly.
There are actually very few characters with wavy hair in SNK. Most of the Eldarians have straight hair.
No one around her has wavy hair. Levi has straight, so do Historia, Eren and farmer.
But look closely at the Ackerman family.
If you line up the Historia's daughter here, it is clear that she has Ackerman blood in her veins.
Note the clothes she's wearing.
Isn't it unnatural for a child to be wearing a dress with a hood when it is not a raincoat?
Speaking of hoods, when Historia spoke to farmer, there was someone behind her.
I have explained in previous posts that this person's identity is Levi.
Historia's daughter has a hooded figure (Levi) involved in her birth and she wears hooded clothing to remind her of this.
She has strong wavy hair and the Ackerman family also has wavy hair.
She is of Ackerman blood. She is Levi's daughter.
PS: We don't know the colour of Levi's father's eyes, so even if daughter's eyes are a different colour to Levi's, it doesn't negate the fact that her father is Levi.
PS2: I've had some astonished comments that "Farmer's hair is definitely wavy", so here's a picture of Farmer. If you think it looks wavy, you need to see an ophthalmologist.
It may look like the ends of his hair are bouncing, but most characters with similar hair length are drawn this way. It is not a feature of Farmer.
Farmer's hair is straight.