I assume you mean Platinum since she never changes her pokemon when she appears in any other game.
In Platinum, the various gym leaders and E4 members who will have rematches against you after you get the national dex never change their pokemon after the first rematch. What you saw her use against you the 2nd time you fought her will be exactly the same for every single time you face her from now on.
lvl 74 Spiritomb (Ominous Wind/Silver Wind/Dark Pulse/Psychic)
lvl 74 Roserade (Sludge Bomb/Energy Ball/Shadow Ball/Extrasensory)
lvl 74 Milotic (Aqua Ring/Mirror Coat/Ice Beam/Surf)
lvl 76 Lucario (Aura Sphere/Dragon Pulse/Psychic/Earthquake)
lvl 76 Togekiss (Air Slash/Aura Sphere/Water Pulse/Psychic)
lvl 78 Garchomp (Dragon Rush/Brick Break/Earthquake/Giga Impact)