Ranger is good, but so is Barbarian! She can wear her Medium armor, get a speed boost, go Rage from time to time, and she gets better skills. Ftr4/BarbX is a potent mix.
Or she could pick up one level of Sorcerer and then go Dragon Disciple. (Her two Sorc spells are: Feather Fall and True Strike. They can be cast in armor at no penalty.)
Is her Wisdom okay? Consider Psychic Warrior (from the new XPH -- "Expanded Psionic Handbook"), or Cleric.
Is her Intelligence high? Consider one level of Psion, then go into the Prestige Class "Illithid Slayer" (again, from the XPH).
Does she like burning things? The Pyrokineticist no longer requires any specific psionic Powers, just that she take the "Wild Talent" Feat. It's particularly good for a Fighter who can specialize in the Fire Lash, or who likes using flaming weapons (+2d6 Fire damage at 2nd level). Pyro requires any Chaotic alignment.
-- N