Fast for Alhaitham as much was for Cyno.
What does Nilou bring to the table that existing characters don't? (speaking as a non-Nilou haver).
If you have all hydro chars and at least one dendro on your team, her elemental skill (if you use the dance) will give Nilou and her team mates an aura that instead of creating regular dendro core (hydro+dendro), will generate Bountiful Cores.
They explode really really fast and do more damage than the regular dendro core. You can't make any other reaction on the bontiful cores, so there is pro and cons.
Pro is, enemies can't interact with your bountiful cores, so is get safe for battle against powerful foes. The cons is, you can't either interact with them as well, so using pyro against dendro core or electro with dendro core is useless.
In my experience, I can't see any more utility than curiosity about this mechanic. Is sometimes fun, but is boring limiting your own team. And limit the Nilou composition as well, so she can't make team with others elements if you want bountiful cores.
So, in the end I just use her as a regular hydro and sometimes for fun I put a team exclusive for her.