Tell them they suck at timetabling. Maths and history isn't that unheard-of as a combination.
A-level maths is difficult and even people getting 7s, 8s or 9s can struggle with it. However if you have any interest in an economics/finance related degree it'll definitely be helpful, if not required. With a business or management degree, probably less so.
With history, GCSE performance doesn't affect how you do in A-level to the same extent as in maths, since you'll be studying different topics with different styles of questions.