How does your fantasy race view humans?
They don't like us. In their legends, we're stupid, brutish and disgusting - basically, "human" is their version of "troll". In this case, I'd recommend coming up with new words. It would seem strange to make them use words that mean "troll", "male troll", and "female troll" (except as insults).
They feel a kinship ...
I'm probably gonna be crucified for this given the relative lack of artsiness, but why not say 'landed amid the Zinnia's anthers and covered herself in pollen'.
Anthers being the rods which present the pollen of a plant. Stamen also works, as that's the whole male apparatus of a plant. More here:
A few alternatives:
She dived into the flower.
She dived into the zinnia's flower.
She dived into the petals.
She dived into the zinnia's center.
She dived into the pollen.
Add the rolling in pollen parts if needed.
I realize you want to differentiate between zinnia the plant and the actual flower. You don't want your ...
Putting scientific definition aside, "Flower head" works better since it's a personification. The human reader has no trouble associating the upper part of a body with the upper part of a flower.
On the contrary, "a flower's heart" is a little harder to imagine. Without further context, I would struggle to understand what you mean, exspecially since I'm ...
Speaking as an academic and professor, I say you are right. "authored by" implies sole authorship and denies others the credit they are due. Use co-author, or "John Doe, et al" for specific papers. Or if you are talking about a mix and John Doe is the sole author of at least one, then "authored or co-authored by" is appropriate.