She is from Spain hence from the European Community so she doesn't need to do anything at all.
She could go to the spanish embassy to enrol herself if she was going to stay here in this country but if it is just for the summer she doesn't need to.
With regards to the English schools, there are usually 2 prices, one for european (cheaper) and one for non-european, but all this information will be on the school.
One advise is for her to enrol in any other course as the language course are full of non-english speakers (obviously) and they end up speaking their own language.
She could do any other course (about anything she is interesting on) and where the other students are british so she can make British (or english speaker) friends and she will learn faster.
hope this information help.