Well, apart from the fact that this really isn't that common (sticking to my guns here, there are a lot of details the same ), I'm right there with you in thinking it's a coincidence. My fanfic isn't that popular, so unless she would've searched it out, which I don't think she would, it seems implausible that she took the idea(s) from me.
I do indeed know about the idea that no idea is original

I do follow the writer on Facebook and won a book from her once through a writing challenge of hers, but I'm not going to PM her asking about it or pointing my fanfic out Maybe she doesn't even support fanfic, I have no idea

Either way, I just thought it was a funny coincidence