the second you said, Jill doesn't do anything sexual lightly, she wants to be sure.
I don't think however that the term "innocent" is the most correct for Jill, she is very serious, considering her age also excessively. even when Jill slows down MC's momentum, she seems very aware to me. she is very polite and therefore not very spontaneous, she always does, or at least tries to do, what she deems right. in every aspect, even the sexual one
she is opposites with Bella: Bella lets herself go and then repents, Jill holds back and then consoles herself by convincing herself that she did well