Emily keeps watching, eyes glued to her sister. She feels shame at her sister for becoming...this, but part of her deep inside kind of thinks she looks happy, and free. Maybe she'd like to feel like that one day too.
Kelly, stuck in an orgasmic haze, forgets her sister is standing there watching her. Eventually the bill is satisfied, and pumps her full of cum again and her orgasmic skyrockets one final time. Mooing uncontrollably, her face starts to change. The black and white fur covers what's left of her skin, and her nose extends out and widens, the tip staying slightly pink, and forming a dampness. Her bottom jaw follows, making her mouth bigger. Facially she still semi-resembles a human, just with cow-like features, as like the breasts, it seems she won't fully convert into a cow. But from a distance you wouldn't be able to tell the difference. She still kept her long, bright red hair though, and standing on her hind legs, she reached half a foot taller than her previous 5ft.
Emily stood there in shock, watching her sister lay there mooing in pleasure, cum dripping out of her pussy. There was something kind of hot about how she looked, in a really primal, pure way. Eventually Kelly got up, and trotted over to Emily. She got to the fence and stuck her head out of it, mooing at her sister. Emily had no idea if she recognised her or not, but she reached out and strokes her sisters new face. As she did, a faint, golden haze moved from Kelly's head, up Emily's arm and disappeared.
Emily kissed her sister on the forehead. It was time to make a tough choice. We could leave her here, she looked happy. But could she really leave her sister living on a farm, even if she was a cow? Maybe she should tell Mum and Dad...