Is there a considered difference? Like, if I want to lend one of my painted pets out adn I get to borrow one in return, does that count as trading? I am sort of confused by the language because of what pet trading means on another site.

I would consider that trading, personally and I wouldn't risk it. You can't transfer the pets back for 30 days, so you wouldn't be able to just send one pet back and forth, then send the other back and forth (which imo is less suspicious looking than just swapping a pet one way and swapping them back in a month). The best way to find out would be to file a ticket though

Yeah, looks like I'll be filing a ticket. It's too bad to, because I have a lot of colours my sister doesn't have and vice versa and since almost all of my pets are permanent, that means that I'd have to potion/paint one of them a billion times. xD

Trading pets is against the rules ^^' https://subeta.net/help/rules.php?act=rule&id=33

If I'm wrong then the rules need updating.