Honestly, your mum gave you a home, a family, a life and unconditional love, despite her grief

That's not an optional thing. She chose to adopt, and unconditional love is certainly questionable in this case. Sure as fuck seems like there was a condition, "you will listen to me talk about my miscarriage in graphic detail from a very young age irrespective of your feelings on the matter and act like my therapist and be constantly reminded that you are acting as a replacement before you're even old enough to understand any of this."

However, instead of growing and maturing and seeing the situation from an adult point of view, empathising at how awful it must be to lose a child and how

And none of this was inspired by her Mum's unabashed emotional neglect? She brought none of this on herself because of a fetus she lost 30 years ago? And because that fetus existed, OP deserved to constantly be compared to it and made to feel inferior to it?

Meanwhile the Mum has to do absolutely no introspection about how her actions toward a child she adopted at young age have clearly given OP trauma?

This whole "consolation prize" issue is yours, I would bet she feels nothing of the sort.

I think the OP probably has a much better idea of how her Mum portrayed this whole situation to her and you're just going to sit here saying "nah none of that actually happened you're just mad" like you know her and how she was treated from a young age?

You have no idea what her life was like. Don't you dare act like you're some sort of master psychologist about all this when we only have a very general overview.