If it is his daughter then I feel it would say that in her part of the script. Personally I wouldn’t mind if it’s a sister. A bond between siblings is just as strong as a bond between parent and child. Especially if said parents are not there, so the siblings are all each other have.
Violet is also not that intriguing of a character but then again neither is Henry to give adult versions of them big roles in S7. Henry I could see but I feel both characters need to be connected to main cast from today and it wouldn’t work if it’s just father/daughter.
I also feel people will not take kindly to a direct rip off of S1. Yeah the parallels will be nice but they’ll just basically see this as unoriginal and a carbon copy. Making the little girl a sister at least adds a different dynamic. Rather than a genderbent S1 storyline.