Talking to Gawain, we figured out that it should probably look something like this:
Thunder Child template (Advanced Bestiary)
LA +1
Dex +2, Int +2, air breather, Auran language known, racial HD change, +1 dodge bonus, electric grapple, SLA 3/day (fog cloud), resist cold 5, +4 racial to Knowledge (nature) and Survival, Quick Draw feat
LA +2
Double speed, +2 dodge bonus, electric aura, electricity, SLA 3/day (gaseous form), cloud sight, resist cold 10, breath weapon 1d4 electricity, Improved Initiative feat
LA +3
Dex +2, Wis +2, +1 dodge bonus, breath weapon 1d6 electricity, SLA 3/day (sound burst), immunities, lightning jump, Lightning Reflexes feat, elemental type (air, extraplanar subtype)
The PC will allowed to take a "level" and buy it off when she earns enough xp.