No there won't be an explanation as to why she's that strong. She's just much of a monster from birth that its why she grew up to be an emperor that no one wants to fuck with.
I could give three fucks about an emperor. Luffy is the future Pirate King and he was strong as a kid, but that's it.
@Lao:
You're setting yourself up for dissapointment then, because while I can imagine we're gonna get some insight into her abnormal size, I don't think we'll find out why exactly she's this strong.
It's honestly better to just go along with it, and it's not like it's the first time kids excercised this kind of strength in OP, Zoro was lifting huge boulders for hundreds of times when he was just a kid, and he was normal sized. Kids from Punk Hazard were ripping off chains and the bigger ones even sent Luffy flying. Linlin's just naturally strong, no point in thinking too hard about it.
Except Zoro was going through a hell of a training regime, is it even necessary to explain this? Zoro was training all the time, which is how he could beat all the adults at the dojo and lift a boulder like that one, which by the way is nothing spectacular. However Big Mom just appears out of nowhere as a 5 meter tall child capable of murdering all the giants in an Elbaf town.
Let's also remember Elbaf is a warrior nation, just like Zou and Wano.
I'm convinced 5 years old Big Mom is stronger than every single opponent Luffy has defeated prior to the timeskip. By far. And this needs an explanation. She's a chemical abortion by Vegapunk or something.
–- Update From New Post Merge ---
Chapter title already explain everything "Natural Born Destroyer"
That's rubbish. Why is she a natural born destroyer? I can't believe you are not questioning this?