Thank you all! 
I have absolutely no idea how he's doing with the work, though.
He's not particularly informative unless it's about Pointless.
We've have applied for a discretionary bursary for him today from college. There were lots of criteria about benefits received, and me receiving working tax credits and earning less than £16,000ish per year meant he was eligible. It'll mean he'll get about £15/week term time, which will pay for his bus fare and lunch.
I think I missed a trick the last two years as DS1's sixth form had a similar bursary, apparently. It might not affect anyone on the thread but if you are on a low household income it might be worth asking the question.
BOOP, I hope you and your DD come to a decision this W/E. My DS1 did stick with 4 subjects up until AS and dropped one for A2, but with the linear A levels it's more tricky. The school used AS levels to help predictions of grades and I'm sure universities used them when deciding on whether to give an offer.
But 3 A levels were all that was needed to get his uni place. Some unis give slightly lower offers for 4 relevant A levels, eg AAAA instead of AAA at Warwick for maths but getting 2 A grades in physics and chem sounds harder than getting one A in physics or chem.
I guess unis that are offering on UCAS points rather than specific grades it might be beneficial to do 4, but it depends on your DDs plans. I guess you've been looking at entrance requirements at a few likely unis for courses she might be interested in? Just to give you a feel for what's the best option?
It was definitely the right thing for DS1 to concentrate on 3 in Y13, even though he did maths and FM which is quite often a combination that means students do 4. He did very well in his 3 and I'm sure he could have done pretty well with 4 as well but may well have dropped a grade in FM, which would have meant not getting into Warwick.