I’m not sure how far she could get, but I’m pretty wary of launching her up to Saiyan levels of fuckery. She’d probably be good at coming up with new ways of utilizing ki, though, and her repertoire would expand very quickly. 

For example, since Sunset is a Unicorn around Twilight’s level, there’s a very good chance that she knew how to teleport. That could carry over to the DB world. I don’t think it’d be around the levels of hax that, say, Instant Transmission would be, but she’d probably be able to teleport a decent ways away. Good for getting the drop on unsuspecting enemies, at least. And not in the same kind of manner that other fighters sorta use their ki to flash step, either.

As far as raw output goes, magic being the equivalent to ki would let her shine in this regards. Magic-marked Unicorns usually have an edge when it comes to stuff like that anyway. Twilight, Sunset, Starlight, etc. So, dumping ALL of her energy into a blast might come close to Final Flash levels of pants-shittery, even though it’d take literally everything she had to do it. I’d definitely say she should black out after something like that, though. Actually, if there’s one thing that I’d probably compare to a Saiyan, it’d be ki output.

As far as control, of course she’d be able to use telekinesis. It’d actually probably help her find interesting angles to attack from. Such as storing ki in balls to fly them around and then expelling them in beams aimed in a certain direction. Like imagine getting hit with two or three mini-Masenkos from different directions at the same time. I think that’d be kinda cool. Like ki versions of funnels from Gundam.

I like the idea of using Daydream from a visual standpoint, even though it’s not really something that SHOULD come about without the inclusion of Friendship Magic and the influence of the Elements of Harmony. The energy from her forehead and her back just makes for a really cool and unique look. 

ULTIMATELY, I think that Sunset’s strength would lie in her usage of ki instead of anything more physical, and she’d probably realize that. She’d train her body, of course, but I highly doubt she’d get super buff and roided out like a lot of the DBZ crew. She’d probably be way more interested in ki manipulation considering it’s kinda like magic, and she could just use barriers to shield herself from most kinds of attacks anyway. And yeah, she’d probably understand why Celestia would withhold information about the mirror and beyond if it connected to a world like this.