Your case is complicated, and so it's difficult for us from different countries in different legal areas to help you. You combined different flights on your own? You booked in Spain? Via BA website or a travel agent or any other booking site? What law applies then? EU law might help you.
And if your wife has special needs, you should take care of ways to ensure those needs before booking. I'm sure european airlines usually support many ways of transporting passengers with restrictions.