It's a spoiler because it's information about future plots or events in the show (the appearance of a character who is not a main character). It wasn't a guarantee that she would appear. I agree it was a minor spoiler, but I wouldn't say "of course" she would appear just because the actress currently doesn't have another job lined up. I'm not even upset by it. I just found it amusing in contrast to the post immediately above yours which said the same information but was careful to use spoiler tags. That's all.