It's marketing of course but she's a headliner in R&L terms but yes I imagine she will play before Hozier. Same as their 6 headliner thing from the last few years, essentially 3 heads and 3 subs but they still call it 6 headliners.
Semantics anyway, I don't care about R&L but if she plays Glasto I will be ecstatic. Lineup is shaping up to be an all timer.
As things are standing right now, this will be the final 4 of the main. But not every act is a 100% for each spot right now, some other things still in the works.