Re: Unilateral Pes Cavus
If the 4th metatarsal is painful, then what pathologies could it be?
If she's had a previous stress fracture, i'd be thinking another stress fracture. Xrays can be inconclusive for a few months.
From the info you've given, i'd put her in an aircast for a few weeks and let it calm down. Long term- once its healed, custom orthotic with modifications to reduce bending forces on metatarsals.
What are your suspicions? Neurological conditions? CMT?
Mackay, Queensland Australia