Yes! “Surfer” is gender neutral, so just say “I imagine that the surfer who was attacked…”

And second, this is small, but when you say “I imagine that” you are speculating; you’re not sure. But then you say, she “must” be holding a grudge, which is more certain. So I would say this, to keep the whole sentence uncertain: “I imagine that the surfer who was attacked in Bali is holding a grudge.”

I don’t know the story, but you would hold a grudge against someone you know.

Love that! Same with me, I went to Spain, thinking my high-school French would help me (?!) and obviously it didn’t. You would want to say, “I couldn’t understand anything” or “I couldn’t understand a thing”