Whilst her Swedish 16+ are probably a vey loose equivalent of GCSEs, and she would be accepted to take A levels here if she has sensible grades (acceptable for preparatory Gymnasium level in Sweden?), any Sixth Form would probably suggest that she takes GCSE English alongside any A levels, and probably a Maths qualification simply to make her pathway to Uni or employment easier.
Many Sixth Forms do accept late applicants - which city or part of the UK?