I’m sorry, but you cannot make a joke in the first episode about Rachel not knowing which one of her dads is her biological father with an image of a white and black guy, and then cast two white guys in season 3 to play her dads. that’s just unbelievably inconsistent of them.
Yes, Shelby is a surrogate mother, not a biological mother who gave her child up for adoption - it’s different than Quinn.
But Shelby does owe Rachel something because for her own selfish reasons she forced herself into the girls’ life only to reject her - a girl who has had that her own life. Shelby is worse - she’s an adult and she did this knowing what this action would have on Rachel.