Could this also be "She is a potato"? (lol)
Depends on your opinion. She wouldn't like to hear that. :)
Yes, but not a friendly one after she hears this. :-)
Could it be "It is a potato" instead of "This is a potato"?
Yes, that's an accepted translation.
I think the answer is no.
Αντός - He
Αντή - She
Αντό - It / This
Sorry, the words you wrote do not exist. You used the letters....
αυτός -> he, αυτή ->she, αυτό ->it