You have a healthy attitude to life Belinda and I wish it could rub off on me!
Regarding English, I think that everyone could benefit from it being compulsory, though not necessarily examined, if a child wanted to stay on until 18. Can I ask what school your child goes to? Certain independent schools that do A'levels or the Pre-U spend about 30-40% of the timetable on non examined subjects such as English, politics, religion and history so they are still developing their written skills. In some schools is called 'Div'.
If your child does very well with the IB then she will get into good Uni's although I think she may find it difficult getting into the very top ones for science if she's up against students who often have 4-5 A'levels in the maths and sciences. If she had three strong science A'levels then I think it would be less tough. The other thing is that its not just about getting in to uni but how well prepared she is for the course. If she sticks with science she may find that she is behind her peers or has a lot of catching up to do with the IB.
Many independent schools opt for the IB as a way of competeing with other independents as they offer an alternative, so any school offering it will always give you their biased view, as would a school that offers only A'levels. The last thing to consider is your daughter probably has more chance of getting top grades at A'level than she does at IB because there may well be some subjects that she just does not do as well, so that may be something to consider.
If your daughter wasn't keen on science then I would have said that the IB will be fine, but maybe further research may be beneficial. Good luck with your decisions - I'm sure she will do well with whatever she chooses, and maybe you can come back in 2 years an tell me I was talking rubbish!