Spoiler
First thing, the royal are not scums
She is the princess but the reason why no one remembers her is because her mother belongs to the race that lives on through memory. Since the princes was only a halfling, the mom received God's punishment and died and when the mom died all memories of her including the mom's pregnancy and birth were all erased. That is why no one knows about the princess because they didn't know she even existed hence she was living in a abandoned place for a long time. The royals later on made up for the lost time and doted on her.they even feel guilty for forgetting her even if it was not there fault and it could be helped that they forgot.

she is by no means abandoned it will be explain later unless you want spoilers