I don't think we know for sure if Mirror Weiwei has lived in Dixing before? Either way it's definitely a reasonable interpretation that she hasn't.

She must have grown up with her father enough to remember him - he officially died before she was born, so I assume her mum joined him in secret wherever he was hiding, whether that was in Dixing or Haixing or neither. (If one of them also had mirror powers, she might have grown up neither in Dixing nor in Haixing, but inside the mirror realm, which would be a super weird childhood! Or she mighit only have ended up inside the mirror after she developed her own powers. Either way, I'm not sure she'd want to go back to living inside a mirror, being able to look but not interact. She'd probably prefer Dixing ...)