Well... all I can say is that present "Rena" (which seems to be Itsuki) may not 100% be past Rena...
However, I am also lead on to think Itsuki was going to talk about her "food reviewer May" persona (and the clothes by a fluke happened to be the same as Rena)... but yeah no, even I'm at a loss of words. It's English here, so some words may have been "lost in translations" but that's doubting something just to hold onto a faint hope that Rena was someone else. Not that Itsuki being Rena is a bad thing, but is... well tbh not exactly intriguing choice. As some others have already mentioned in one way or another, the other Quints would be much more glorious in the sense of doing something different for "who was the secret girl."
(Also, F to people who say "this is the way of harem," riding a rollercoaster of basic tropes as if those trends equate to good stories, which I believe is false)
And yes, I'm here on SS Yotsuba, lagging behind, wondering why Negi aint feeding her the same amount of fuel as the other ships... that credits page hit too deep in the heart...