You are extremely empathetic from what I am reading. I think it is good that you try to understand why she has done what she has.

Jealousy is normal between siblings but in my experience it doesn't normally have such extreme affects into adulthood. We normally grow and develop away from this. It sounds like she has harboured an unhealthy attitude towards you for a very long time.

I guess your choice now is whether you include her in any shape or form in your life. If you choose to keep her in your life please take care.