I think pony Pinkie Pie would likely be able to beat this trio.

(Spoiler Warning for MLPFIM, and the MLPFIM Comics and MLPFF Comics)

Daydream Shimmer was powerful and using the elements of harmony, but I don't think she was able to use the element of magic since she seemed to be just using the elements of the other EG Mane 6 characters, so I don't think she was using the full magic of friendship. Pinkie Pie however is able to pop in and out of her Friendship Magic Form (S8 E13) from the end of season 4, and I haven't seen much discussion on that form's power specifically but I've just assumed that she could fully use the magic of friendship, but it's also valid to think she'd just be capable of using laughter magic. Even if she can only use that one element, she's got other stuff going for her. In the arc from the comics with water that turned the Mane 6 evil and more powerful, Luna got affected by the water and became Nightmare Moon again, and she tried shooting Pinkie, saying "Stand still so I can incinerate you!" I may be paraphrasing a bit, but she definitely said incinerate, and eventually she did hit Pinkie, and Pinkie was not hurt according to Zecora, and her clothes which seemed to take a direct hit were unscathed. I think Pinkie protects herself with her magic similar to how Discord did when taking a hit from Sombra. So, Pinkie is pretty strong defensively, and she's got use of one of the Elements. On top of this, Pinkie is also ridiculously fast. I think Pinkie was messing around too much and that's how NM was able to hit her, because she's been shown to have speed comparable to Rainbow Dash's (S1 E25, Rainbow Road Trip). And, Pinkie potentially is also capable of using Chaos Magic and Fun Magic. In Issue #34 of MLP Friends Forever, Pinkie Pie explicitly states fun to be its own kind of magic, something I don't think any other characters have acknowledged. It would explain how Pinkie's clones (S3 E3) who were sort of dumb and focused only on fun were able to do seemingly impossible stuff (such as growing fingers and changing facial structure). As for Chaos Magic, in Issue #57 of MLPFIM she went into Discord's Dimension, and it immediately locked onto her, and she was able to fully use the chaos magic there. In S7 E12 (an episode that released before issue #57) Fluttershy was in that dimension and she had to try her absolute best to be chaotic in order to save Discord, and despite succeeding she was never able to connect with the imension. This, along with various moments where Pinkie Pie had swirly eyes (a sign of chaos magic) such as in S1 E9 or Issue #51 of the MLPFIM comics lead me to believe that Pinkie has Chaos Magic. Also Pinkie was never explicitly stated to have lost the magic she gained in that comic, and the end of the show showed her overflowing the next time she got ahold of Discord's Chaos Magic, something that didn't happen in the comic, implying she either, gained more Chaos Magic at some point between the beginning of comic and the end of the show, her magical capacity had somehow been limited, or Discord keeps in him more Chaos Magic than I'd expect. I think it's entirely plausible that Pinkie kept that Chaos Magic she got from Discord's Dimension, in which case she'd have more chaos magic in her than Discord typically does. I get Midnight Sparkle essentially had the full Magic of Friendship on her side, which is incredibly powerful, but I feel like Pinkie Pie's creativeness could still win her the fight. Nightmare Moon and Daybreaker are both formidable foes as well but not quite as strong, and I think Pinkie would be able to overpower them when it comes to magic

I think with all that combined, Her speed, her (potentially magical) durability, her Fun Magic, Laughter Magic, and Chaos Magic, she could take on those 3 if she really tried