If I had a sister like her, she'd encourage me to. My sister and i tried it, but didn't continue. One of my female cousins and I continued into adulthood screwing, while she was married and fucking her married brother, as well. I could never be sure what I was eating out of her pussy.
Who said that brothers and sisters can't have a relationship?
My brother and I used to think like that in the beginning, and after the first relationship with each other, which was very enjoyable, we were shy for a while.
But we started again and we are still continuing and we are satisfied.
In my opinion, there is no relationship more enjoyable than sibling adultery.