Please can you advice if the subject Statistics is worth doing for GCSE outside School. My DD loves the graphs and data analysis areas of it and confident that she may get higher grade. Is this going to be an extra burden on top of what she already have from the school and of any value in having an extra good grade?

No it isn't - focus on a good grade in Maths.

DD is good in Maths and good grade is expected. We are trying to see the advantage of doing a subject she loves outside school, if the chances of getting good grades in it are reasonable?

Honestly - my son is doing Statistics as one of his GCSEs IN school - yes he enjoys it - yes he is taking 11 GCSES. Does he need to do any more outside school? Absolutely NOT. Universities only look at your best 8 anyway.

If you feel your child needs stretching because the school work isn't doing this enough, then challenge her to do something outside of her comfort zone - volunteering to help others, getting a job, learning a sport, playing a musical instrument, drama, swimming, exercise, cooking etc etc - the list is endless! All will help make her a more rounded individual, will make her more confident in herself, will increase her self esteem and self worth and are likely to make her a more attractive candidate to any university or employer than someone who is just increasing the number of GCSEs they have.

I am considered by my peers to be an 'expert' in maths education and can assure you that there are far better ways of enriching her mathematics.

UKMT challenges are a good start, NRICH website and there are some great books by Rob Eastaway such as 'Why do buses come in threes?', 'How long is a piece of string?' ....

There's so much maths out there without taking further GCSEs.

I also agree with KCG that sport, music, volunteering and other extra curricular activities should also be considered.

Agree with all of the above.
Two of my DC's had to do it in school due to being good at maths but didn't feel it added much.
It did give them a bit of a head start in that module at A level but as much could be achieved by a few days looking over subject in summer before year 12.
Definitely wouldnt go out of one's way to add it on.

My copy of "Why do buses come in threes?" was lent to various friends of my daughter, the last of whom never returned it There are books like it that have nice worked examples and puzzles you can work through if you enjoy a mathematical diversion.

I also agree with the suggestion to consider other, extra-curricular activities because they'll enrich what can otherwise be a very one-dimensional academic applicant to a job or university degree, can give an insight into certain professions to enhance or deter someone perhaps interested in it and generally make for a more rounded and interesting applicant and colleague.

+ 1. Universities are not bothered about dc who have crammed an extra subject because they (or their parents) may think it looks good.