Just because Lóránt didn't give permission, it doesn't mean the demon can't try anything.
Lóránt made a gamble, and while it brought the expected result (Unn feeling better), it also brought some unwanted consequences they'll forever regret.
Lydia was thinking that Nessa would eventually get her diary back and read through the notes. Or just trying to feel Nessa's presence in any way she could, thus messing with Nessa's things.
You seem to have a bit more sense than Lóránt if you can think about talking to "superiors". That said, Lóránt hasn't got a direct boss as such, and even if they did ask for permission, Zhofie's background means nobody in their right mind would allow this.
And thus we have Lóránt's moment of Good Job Breaking It, Hero...