Sostenueto I hope your DGD has a brilliant time in London, its such a great city for sightseeing and shopping. Very selfless to keep your illness to yourself while she is doing her exams, I wish you all the best with the treatment 
Alexander its good to hear your DH is doing so well health wise, but not so good about the washing ..... hopefully the delicates survive
Lobster is absolutely right about how its isn't necessary to do any more than 3 A Levels, although many maths scholars will take Additional Maths as a fourth. University entrance is based upon 3 A levels and three good ones are better than 4 mediocre. A economics degree is maths heavy and most will require either a very good GCSE Grade (7 or above) if not taking Maths or a maths heavy science to A Level. Its worth looking at course content and structure to determine how much writing is involved, particularly the range of options, as some will have a final dissertation and others will not, allowing the student to choose.
DD is struggling to focus today, keeps breaking for a snack or to ask an unnecessary question!