As a Bloom Support, Nilou's role is to maximize a team's Bloom Damage in teams of strictly Hydro and Dendro characters. Level 90 is highly recommended to maximize Nilou's HP and Bloom Damage
Regarding Weapon Choices:
Serenity's Call: As Nilou only needs this weapon for the passive, it can stay at Level 1.
Regarding Artifact Choices:
Sets
Deepwood Memories (4): Can be an option if other teammates are not holders.
Substats
HP%: Prefers HP substats above all else until you reach the limit of her A4 passive which is at 74444 HP
Regarding Talent Choices:
Talent levels do not affect Nilou's buff to Bloom damage, so heavy investment in Talents is not necessary