The character Hariet did not originate from fanon, and the information on this page may not be entirely accurate to their canon. You may read more about this subject in the context of their canon on the following wiki(s):
Hariet is a bombs expert and is responsible for the pyrotechnics. Hariet is considered to be the least predictable of the Broodals. While normally wearing a small doll hat, she brings an iron helmet in battle, in which she stores her homemade bombs.