I always found it weird that Peach was one of the most technical characters in Smash history. Her float, while originally designed to make horizontal recovery easier, has always been a source of hard-to-pull of combos and insanely miniscule microspacing. Item play, which Peach also has in form of the Turnips, also brings along one of the longer lists of advanced techniques like glidetossing and z-dropping.
This is always why I thought Daisy would be the Lucina to Peach's Marth: A more accesible version of a beginnerunfriendly character. In Daisy's case, that means doing away with the float. Not only is it never used by Daisy and the closest thing Peach has to a signature move, it's also unneccesarily complex and cutting it would allow Daisy to be buffed in areas like movement speed, to closely match the stat differences Peach and Daisy have in Mario Sports games, with Daisy being more all-round oriented than Peach's technical statspreads.
Super Mario Run would later give Daisy a perfect alternative in the triple jump. It would radically change Peach's playstyle even without changing a single move. Instead of precise microspacing, Daisy wouldn't have the patience to minimize her movements. Instead she would jump right in with either her Side B (Which would be the Flowerbed Return of Mario Power Tennis) or her triple jump ability. Faster movement, at the price of being much less precise.
For Specials, making a Daisy moveset becomes harder. As you said, most of her stuff is one-and-done or just a part of the games she's in and shares with fellow party guests and tennis court combatants. However, there's one move that returns as "special move" in spin-offs when it comes to Daisy: A Flower Garden. Present in Mario Power Tennis, Mario Sluggers, Mario Sports Mix and Mario Golf World Tour (albeit as a victory animation), Daisy creating a garden is one of Daisy's more recurring powers and one that is obviously associated with her general flower affinity too (unlike Mario Strikers' Crystal Smash).
It'd fit in with her general playstyle too of being grand, rigorous and not subtle. Her space is her space and she's not letting it know by throwing a Veggie or strategically floating around the opponent, she lets it know by letting her namesake flowers grow on the battlefield where she stands. Now, stage control elements are dangerous to implement in Smash, because zoning is a very easy playstyle to adopt and very little characters have powerful stage control options, so the Garden couldn't be something that damages or slows opponents. Daisy's need to approach would diminish and Daisy is the last character that would wait in a fight. Instead, Daisy's Garden would need to make normally unsafe approaches safer, by giving Daisy herself a speed bonus, or reduce landing lag on key moves like her "Daisy Bomber" Side B.
Now Neutral B/Down B would be a sports ball (depending or whether Garden would be a neutral B or down B), but not just any sports ball. Smash often takes inspiration from debut games so for Daisy, it'd be none other than Super Mario Land's sole power-up: The Superball. Bouncier and more erratic than your average ball, fits Daisy's bouncy and energetic personality and playstyle. They'd lose the Turnip's property of being an item and would be a more self-sufficient projectile like Mario's Fireball which would take away a part of Peach's technical skill floor.
Being more bouncy, they're perfect for in your face volleys, combos, or covering all-in rushdown approaches. Bouncing off of walls and shields, they can really put on pressure, again, much more visible than Peach's mindgames.
If you forego the premise of Daisy being "Easy Peach", the Superball and Garden could work together by giving the Superball a special effect after it bounces in the Garden. Lip's Stick's "Flower" effect is a prime candidate and can also be implemented in different moves to give Daisy damage without having to memorise float-specific combos, and can be a balancing tool to offset the fact that she's Peach without the peach de resistance.
For normals, she can be a bit more rowdy and rough n tumble. Although she'd still be in the dress, she's not afraid to lunge, tackle and dunk her way through the competition. Melee Peach gave us some headbutts, kicks and explosions that could return to Daisy and even though Daisy is not a full-on brawler, she doesn't shy away from the occasional uppercut.