Since she used to have an iPhone, yours still believes it can use this contact as an iDevice.
I would suggest completely deleting all of her contact information, disassociate from her and never speak to her again.
Seriously, try deleting her contact entry and then create a new one for her. See if that works.
This. I've also had luck going in and changing the contact so it's not showing as an iphone. ie not deleting it, just modifying it.
If shes not in your contact list, add her, and delete that old conversation.
