It may also mean that she's not sure why, and that's okay. "Because I want it that way" is the safe answer here, I think, and it sounds like that's what's going on.
FWIW, the more you say about it, the more normal it sounds to me. I just didn't want to dismiss it out of hand as harmless, you know?
But it sounds to me like a very normal--maybe even typical!--control issue for a GT 3yo. I wouldn't recommend making a big deal of it. Then it just becomes more of a battleground for her to stand firm about. I don't think I'd even recommend that you ask her about it further. Unless it scares her, I'd say accept what you con tolerate and then no more, but don't make anything of it with her.
Where shall I send my bill for the utterly amateur psych consult? LOL!
