I know jadis discourse has already been done to death but...

I haven't reread the story in a while but something I've always been confused about is how jadis' knowledge works in relation to fate and the maybe sword. I know jadis is aware of EVERYTHING that is fated to happen and I am not questioning her as omniscient but wouldn't everything that is fated to happen​ happen every time perfectly? How is a character like Allison or Maya able to change fate ​​if the events that are set in stone are already known, and if they did change the events then wouldn't jadis know that? Wouldn't Allison "changing fate" already be known therefore becoming "fate" in it's own right? I'm sorry if this doesn't make sense it's just something I've never understood​​​​​