I would say yes, in theory, but that fledgling would have to be even more important than Zoey Redbird, imo. I don’t think Nyx sees a reason to gift a fledgling with that many gifts/affinities, unless it were an apocalyptic-situation.
I would say the number is infinite. Zoey was gifted with all natural elements at once, same with Other Kevin. I don’t see why other fledglings would be limited in how many affinities they could possess (natural or other (horse affinity, poetry, music, etc.)).
I see pros and cons with both. With a movie, they’d cut out lots of meaningful scenes from the books, but it could wrap up the series quicker than a series because of the amount of books there really are. However, I feel a series (if popular) could really explore the characters and development. With enough luck, it could become the next Supernatural with many seasons. Each season could be a book, imo. So for me, a series would be better.
I feel another event would just plummet her to darkness anyway. She seems like the type of person to let revenge cloud her mind whether it be a minor bad experience or a traumatic one such as her traumatic experience in the novels.