I'll be honest. In the past, I've argued against Daisy being a separate character, and even now, I wouldn't suggest her being given her own slot, but I want to make an argument in her favor. I do not think she would likely be a Peach clone.
While the potential is always there that Sakurai wants to fill a slot and Daisy happens to be an easy target for doing so (like with a third of the Melee cast), I think that if she's added, it will be immediately apparent that giving her Peach's moveset just doesn't make sense.
Peach's moveset is unabashedly girly, and while Daisy doesn't mind being a little girly, she's much more of a tomboy, when she has the option to be. Other than that, some things just situationally don't make sense. Let's see some examples:
Neutral B- Peach pulls a Toad as a form of counter. This makes perfect sense for her, as she rules the mushroom kingdom, but Daisy doesn't command the Toads, that I'm aware of. If any denizens of Sarasaland had been established in the series, you could just swap them out, but to my knowledge, no such thing exists. As such, it makes far more sense for Daisy to use some form of ball-and-bat, as she's featured prominently in the Mario Sports series, including Sluggers.
Up-B: Peach pulls out a parasol, giving her effectively a third jump, a cheeky way to kill off the top, and a lot of horizontal recovery distance, provided she's facing the right way. Now, Daisy, I believe, has beeing depicted with a parasol, in the past, but does daintily floating down really suit her all thay well? Nah, I don't feel like it does. In fact, I'll go ahead and say that Daisy probably isn't as floaty as Peach, in general. Now, I've seen some suggestions for a Rosa-like with hitboxes or some kind of flair jump, but I can't honestly come up with a sensible recovery on account of how little I know. Going with sports references, perhaps a pole vault, but I'd be afraid of making her "Mario Sports, the character" as I feel WFT already does a good job of representing sports as a moveset.
Up-smash: Peach lifts her hand in the air and does a twirl, attacking all around her with a rising ribbon. Cute, but ribbons don't seem like Daisy's thing. I think a flipkick like Fox is more fitting. Or even Wolf's scissor kick. (Rest In Waffles)
Down-Smash: Peach twirls on the ground,attacking those on either side with the skirt of her dress. Daisy can do this, if she's wearing her own dress, but given a more athletic moveset, her more athletic outfit would make sense, or could even be a good alternate costume for her. As such, a splits kick would be more fitting, or perhaps a leg sweep or axe kick. I would go with the splits kick.
Down-B: Peach pulls a turnip from the ground, giving her an item to toss. This directly references Super Mario bros 2 (US), a game Daisy was not in. Daisy can do just about anything else, here. Pulling a turnip doesn't make sense for her.
In a way, I think Sakurai had shown us he feels the same way I do. Daisy is NOT a costume for Peach. Peach has an alt color that references her. Same way as Wolf isn't a costume for Fox. Sakurai probably dodn't think it made sense for Daisy to do all the same stuff Peach did, so she doesn't. Meanwhile, Alph being Olimar and the Koopalongs being Bowser Jr works, as there isn't much of an attitude or tool difference on display.
Now, again, if Daisy is a last minute addition, all bets are off. Ganon still plays like Falcon, for god knows what reason (no sense changing it now, I guess), and most derivative characters start as clones and back away from it at various speeds. Daisy may be a clone regardless of logic, but given the time and attention Sakurai prefers to give characters, I don't think it would end up that way.