Also, it's not like we're born with DNA testers. There's no reason why our instincts actually know the difference between our biological kids and others we've been with, played the same role with, and raised the same way.
There was always an obvious difference in the way she bonded with my mom vs her biological mom. It’s still family, but more like an aunt at best. Despite never saying it, it’s pretty obvious my mother obviously views us differently as well having basically had no say in any of her step daughters formative years.