Yeah, I know, I know, but hear me out.

I've never completed the tutorial, so I thought I might as well do it. Then I got to the "play with the Red Ball" step, and got stuck... because my pet is too happy to play with. I haven't been on this site for a good 5 years, so I don't know how the hell she's so happy after being left alone for so long, without food or anything. I heard minions make a pet happier, so I removed hers. But is there anything else I can actively do to make her smile upside-down?

Yeah, more or less just remove the minion and if your pet is in the resort take it out and wait a few hours for its happiness to decay. I think there’s a weapon (Malerias Clawed Glove maybe?) that has a chance to make your pets unhappy if you use it in battle, but just waiting will also do the trick.