Responses
There's still confusion about this? This is how fan speculations spirals and the cannon becomes questioned.
http://www.mangago.me/read-manga/naruto_gaiden_the_seventh_hokage_and_the_scarlet_spring_month/md/naruto-gaiden-the-seventh-hokage/10/17/#sthash.nRNAmz5v.dpuf
Just look at the bottom half of that page and it explains it. I guess it's understandable if you read it too quickly and get confused from the what Karin meant with "delivered" but it means that she acted as a midwife in that situation. Not like the mother delivering the baby, but as in delivering as helping. Karin is not part of Sarada's genetic makeup at all.
Honestly, i think that maybe after Orchimaru did his experiments on Sasuke, ans he continiously bit Karin for her healing thingy, Sasuke's DNA is somehow altered and he's the one who gave a bit of Karin into the mix... maybe... ╮(￣▽￣)╭