I agree a 75 will do for a while since festae are fairly slow growers, but once she hits 7-8 inches or so, a 75 will get tight.
Females will often grow faster and larger without a male in the tank, mine always remained about half the size of males, but without the male around did not always show best colors.

when I gave her, her own tank, her colors tended to fade. Same female below in her own tank


Females will often grow faster and larger without a male in the tank, mine always remained about half the size of males, but without the male around did not always show best colors.

when I gave her, her own tank, her colors tended to fade. Same female below in her own tank

