Something has just occurred to me out of the blue. When your daughter gets these headaches... are they all over her head or are they localised? (I.e. Can she point to where on her head the pain is worse?)
If she was to have a localised migrane around her left parietal lobe (VERY roughly... just above her ear) this would not only explain her headache but could also explain:
A) Her right arm: Since the Parietal lobe borders on the motor cortex and the migrane is left sided, this may cause unusual feelings or sensations (including pain) in her arm and other parts of the body.
B) Poverty of Speech: The main langauge areas of the brain are in (and around) the left parietal & temporal lobes. If the migrane was localised, then the inflammation could cause a disruption to the langauge centres. Think of a computer network... all the computers are working but instead of being connected with a 100 meg wireless router, they are connected by a 56k modem.
C) Right body pain: See A)
I would be very surprised if there was not something going on and I would happily put money on it occuring in the left hemisphere since the overall body pain is on the right. I would definately follow Carla's advice and seek a second opinion.
Darren