Well, if we're going to be technical, Serena is more like the 6th or 7th female travelling companion (depending on if you count Bianca's and/or Cynthia's brief stints with the group), although she would be the 5th regular one. Interesting in that she already knows Ash, though...

Now I just wonder if he's still going to be stuck as a 10 year old (come on, guys...) or if he's actually gained a couple of years (he seems older in the trailer when he's facing off against the Mega Garchomp, although he seems same as always in the rest of it).