Here is what Urban dictionary has to say, it seems and sounds like it might be correct, but I don't recommend 'Urban Dictionary' as a reliable source. https://www.urbandictionary.com/define.php?term=potato unattractive said by young girls, and with Korean/Japenese meaning also of 'cute'

I have never heard anyone say anything like "She's our potato." Where did you read this? Was it from a predominantly English speaking country?

Johannes // Thank you!!!

I could imagine if you hear Korean/ Japanese girls or Kpop fans using this word, it could also mean cute and adorable, even if not conventionally attractive. Google "kawaiipotato"

Well I've only heard it being used in a playfully derogatory or self-deprecating way before. A girl who thinks she's unattractive might say "Ugh he'll never notice me, cuz I'm such a potato". It's also often used to describe a lazy or useless person "He's a potato, watching TV all day". Although in your example "She's our potato" it sounds kind of sweet