Yay, ophiura is back!! :cheer: :jumping:
Good luck deciding what to do with the anemone. I had a nidibranch that was going to starve in my tank, and I asked on this board how to humanely kill it so it wouldnt starve. Finally, my best friend, a marine bio major, told me that starvation wouldn't be a painful death for the slug--their nervous systems, etc aren't developed enough to feel pain and hunger.
I think if I were you, I'd just keep the anemone in my tank until it passed. That way, you'll at least be able to enjoy it for a little while.