This seems logical for Luster Dawn because she takes after both Starlight and Sunburst. Those two were both socially inept. It only makes sense their daughter would be born that way too.

Maybe this is why they sent her to learn from Twilight

@Shimmering Spectacle
https://www.equestriadaily.com/2019/10/big-jims-q-on-friendship-is-magic.html

“Q: Luster Dawn looks a lot like Starlight and Sunburst. Any relation?”
“A: I say no, but Josh Haber says yes. So, you can decide!”

Considering Josh Haber actually wrote the episode Luster appeared in and her character, he has more say.

@Background Pony #C098

Considering that they generally didn’t confirm it, I’m one of the few who considers it NOT, and yeah some would think that to themselves all they want, yet I don’t think that anyway and another thing, after what sunburst did to starlight when she was a filly, I don’t think she’d trust him that much anymore then that she trusts Trixie, overall.

Well, maybe the next one would be better.

Takes out shotgun It’s the only way…

Maybe you should send her to friendship conversion therapy.

@Background Pony #324F
On the original webpage or this pic, the poster included some info on this. They said:

“I know that some of you are going to say that it hasn’t been made official that Luster is Starlight and Sunburst’s daughter, but really, it kind of has been. Josh Haber confirmed that she is, and although Jim Miller said that he doesn’t like the idea (though he said that he was fine with Starlight and Sunburst being together) since he thinks it makes MLP feel too small if everything kept revolving around the same characters, he also said it can be up to the fans to decide if she is or not. So that’s a maybe/up to the fans from Miller and a yes from Haber. Still, even a single confirmation is enough. And also, seeing that Haber, not Miller, was the one who actually wrote the episode and got his name on the credits, I believe he has more say on the subject.”

@Background Pony #324F
We’ll never know.

Luster Dawn has parents?!