Hi, we've always used: 'сестрінка' when refering to niece from the sister's side, and a 'братанка' for a niece from the brother's side.
We do this to know whom you're talking about. It's more specific. (Many people use these terms.)
Isn't there a difference between a niece from a sister or a brother?
Wikipedia gives specific words only for the sister's daughter: "сестре́ниця, сестри́ниця, сестрі́ниця." I have never heard someone using these.