That's actually my main idea for how Isabelle would work, haha. Inadvertently hurting the opponent and feeling sorry in the process.
Neutral Special: Party Popper - Isabelle lets loose the popper and an explosion of confetti hurts the foe, while Isabelle looks on, horrified. The blast is more powerful if charged.
Side Special: Home Designer - Isabelle lets go of a leaf, thinking it'll turn into a cute furniture piece to make the stage comfier, but lo and behold, they're weaponized! Watch in amazement as foes are crushed by falling couches and prodded by preposterously pointy puffer fish!
Up Special: Letter - Isabelle's letter gets caught in a gust of wind as she holds on, controlling the ascent somewhat.
Down Special: Town Ordinance - Isabelle pulls out a notepad as construction begins on an ordinance. These cycle through different ordinances throughout the fight, rotating between the Keep Smashville Beautiful ordinance (a flowerbed), the Let's Go Fishing ordinance (creates a small pond), and a Let's Find Fossils ordinance (an excavation site). The flowerbed slows down foes who step in it and has the chance to make them be stung by bees for extra damage. If foes step in the pond, gigantic tentacles of an octopus hold them in place for Isabelle's next attack. If foes step in the excavation site, they get the Pitfall effect.
And other things like that. Like, her grab could be her pulling out a fishing rod to go fishing, only to snag a foe (with the pummel being her failing to take the hook off of them), and her Forward Smash could be accidentally knocking over a mountain of paperwork onto a foe. Just quirky things like that, being a sort of different take on the Villager's fight-by-not-fighting thing.
Oh, and her Final Smash could definitely use Resetti popping up and reprimanding the foes, since he's not an Assist Trophy anymore.