Actually it was an error in the rules implementation (although possibly a deliberate one), according to 2nd edition rules, multiclassed druids should abide by the armour restrictions.
And Jalhera is wearing studded leather when you first meet her, so you are free to abide by "will" not wear metal armour if you wish.
Her race permits her select that multiclass option, but has no other effect.
Humans are even weirder. In 2nd edition a human can start out as a druid, with the metal armour restriction, then dual class to fighter, and can wear metal armour. But when their fighter level becomes higher than their druid level they get their druid power and restrictions back again.
But I only mentioned Jalhera to throw another log on the fire...