Hattie is really cute. I had a Dear
America book with
Hattie as the main character's name and it gave me a soft spot. I think it can work as a full name, but it works better as a nickname for
Harriet. I think
Hettie is better for
Henrietta.
I don't know how usable any of these are, but a few other potential full names
HaggithHathorHaticeHecateHippolytaHoratiaHortensiaHyacinthHypatia
~Anna~