She was most likely an overcooked Gem who had to be taught to be perfect by her sisters who had no concept of teaching, were amused by her acting like a Pearl/Spinel hybrid and enraged at her difficultly learning combined with emotional tantrums.
Even if she wasn’t overcooked, she was still highly flawed compared to them and as we saw all the Diamonds were really, REALLY ignorant about everything. Like, even their own powers and how their colonies looked from the ground.
Either way, she had to actually learn everything herself, usually after making huge mistakes. Like learning she is capable of physically harming others by cracking her Pearl, and learning Gems have free will by seeing Garnet form. Learning the Diamonds loved her when against all logic they tried to avenge her death.