Thanks everybody, for all this advice, and the good wishes.
To answer some of the questions....
We haven't been shown the CPR, but it has been read to us! I'm not quite sure why we haven't been allowed a copy, is this usual? The information in it about the BM is very vague. The language they use varies from page to page (e.g. mild learning disabilities are mentioned first, but later this changes to moderate) but there's no real detail about how they affect her, and there's nothing about school or work experiences. There is also very little about her family background only a brief description about her current life.
We are meeting our SW tomorrow so I've made a list of questions and intend to be quite firm about our need for more information. We have both felt that the SW has been very keen to 'sell' this child to us but whenever we've asked questions about the BM etc, they haven't been answered and instead, she's talked about the benefits of having such a young child. I find this hugely frustrating and don't have very much confidence in the information we're being provided. As some of you have said, it makes me wonder if something is deliberately being held from us.
On the other hand, our LA is hugely chaotic with lots of ongoing staffing problems and over the past 18 months it's been hard to get the right information from them at the right time. Perhaps the lack of information is more linked to these issues rather than deliberate obfuscation but it makes things very challenging either way.
Sanders - you asked what we will do with any extra information and this is what we have to consider very carefully. Like you, we have always said that we would like a child who is able to cope in mainstream school and then go on to live independently as an adult. However, while we are prepared to accept some uncertainty and delay, the more I have read everyone's responses today, the more I realise how uncomfortable with I am with the lack of information we've been given.
We'll talk to the SW tomorrow and see if we can get any more information. Fingers crossed....
Thanks everyone for all the advice.