My logic on that is they can't do anything that is too overpowered or unsubtle while pretending to be Dragonbloods in the immediate future and getting reinforcements to fuck us up beyond what is already here would take some time to get through Ceceylne and back. Similarly we kind of have the Realm as ablative armor against more overt attempts to fuck with us by hell.
This means either they have to spend a lot of time finding way to bypass those issues making them a long term problem or they limit themselves to cloak and dagger bullshit.
Knowing that she is a Solar Sorceror in a year means that she is very good but it also suggests that she is both good enough at combat to get into the tournament and has heavy sorcery investment. Being good at both is going to take a lot of xp and charm slots which suggest she isn't going to be focused in awareness or investigation which are what we don't want her to have right now. Sorcery is many dangerous things but subtle isn't one of them which suggests we aren't going to have to deal with it right now except in previously made workings.
Hell is a great threat in the long term but at the moment they aren't here to fuck with us personally and they probably aren't specialized in the ways that would be needed to realize what Nilul is. Also how certain are we that they would care if they noticed. I know the ED told them to look out for her but do they actually care what their bosses runaway daughter is doing enough to risk their other projects?
As for Nilul's fear she is a teenage girl who ran away from home and hid behind someone powerful because she is afraid of her parents. Of course she is going to panic when she sees their agents and identify them as a great threat. She is very good at what she does but she is young and inexperienced outside of her specialties. That isn't to says she is wrong but that she isn't really capable of being objective on the matter.
