I think the set list should be the following:
...Baby One More Time
(You Drive Me) Crazy
Oops!...I Did It Again
Stronger
I'm A Slave 4 U
Overprotected
Toxic
Everytime
My Prerogative
Gimme More
Piece of Me
Womanizer
Circus
3
Hold It Against Me
Till The World Ends
Lead Single from Album 8
Perhaps take out Overprotected and replace it with a different single. If she wants to include more songs, a medley of songs would be interesting to see! The show should definitely be a Greatest Hits show more than anything else, and there should be little to no tracks from album 8 (unless they're singles) so this set list is only 17-18 songs, which is the typical amount of songs for a Britney concert. Once you include interludes, the show should be about an hour and a half.

Obviously, some of the songs will be shortened but that's OK.