I agree xD
It is more a feeling, or maybe what I think it happened xD, anyway, looking at this:
I think that Hippolyta asked Hephaestus to make them after something happened...for example, as a child, she may have lost control and hurted her sisters. That would even explain the emphasis on her being different and on her feeling different from them... Yes...there's the clay thing as the reason why they 'bullied' her, but what if it was also for something else, not only because they believed she was born in another way, but also because they feared her?
After all the amazons hate men, right...? So was the fact they believed she was born from clay a reason to bully her? I don't think they were happy about having a 'father', since they hated men... so...why to bully her for not having one?
Envy...? But maybe also 'fear'...