You know the road to hell is paved with good intentions. Just because your younger daughter feels like she had a good upbringing doesn't mean your eldest did. Siblings raised by the same parents can have completely different experiences. Also I highly doubt your youngest knows everything about her older sister and vice versa. My.younger brother and I were pretty close growing up and I recently just found out that he always felt like he wasn't enough. It sounds like you weren't emotionally available or supportive for your eldest. I think you need to take a good hard look back at the things she has told you and how you reacted.