Fun fact: in the show, they never mention the "valonquar" part of the prophecy, so they're free to kill Cersei any way they want to.
Right. Many of those who push that theory fail to mention that it has never been referred to on the show
I don't think most of us even remember that scene in detail
But from what I've read, GRRM has told them all the key points to hit. So if in the book it is an important detail for who will kill her, the show should follow it. They just decide how that person kills her. I'm sure for a lot of characters, how and when they die wasn't important to the show. Cersei is a different story, imo