I forgot what's with the watch list, why doesn't she want anyone to see it again?

it's list of people she needs to watch out for

It's a lost of people she needs to be careful about, and if the people she needs to careful of find out that she knows they're suspicious then they might try to kill her to keep her silent

so..it shouldn't be bad right??

That's what makes it so bad. She has no idea who took it, so any one of her enemies can find out that she's suspicious of them. If even one of them finds out she could be killed so she doesn't act on her suspicions or anything like that

OH!

But what if the emperor finds it? What would it mean then?

that guard definitely has no right to take that watch list tbh