How much children are affected by hypermobility varies enormously. Lots go through life without any problems whatsoever and find it is actually a benefit (witness David Beckham and countless ballerinas!). Others develop pain and/or mobility problems and may even end up disabled. If you have pain/mobility problems with your hypermobility, you are said to have hypermobility syndrome, rather than just being hypermobile. This may also be connected with e.g. incontinence problems and a tendency to constipation (sometimes also with a tendency to bruise or tear more easily).
My 11-year-old daughter is at this more severe end of the spectrum and has days when she needs a wheelchair. The longterm prognosis is that she may well end up more or less pain free, but that she will always need to do physio exercises and pace her body carefully.
Typically, hms manifests as knee or ankle pains in childhood and/or back pain in adolescence. This may never happen to your daughter, but if it does:
don't panic! the pains are not dangerous, just painful
on the other hand, don't let any doctor talk you into believing that there is nothing wrong with her, that it's all in her mind, that she is dramatising etc etc. Just point out that there is already a diagnosis and insist on being referred to a rheumatologist, a podiatrist,a physiotherapist and an occupational therapist.
Should you ever need them, Great Ormond Street Hospital are THE experts on this condition.
In fact, it would probably be a good idea to have her checked out by the podiatrist and the OT before she starts school, in any case; she may need something minor like insoles or a special pen to help her not to overstrain her joints.
If she does develop problems (and remember there is a good chance she won't!) it will still be a benefit to her to have been diagnosed this early. Many families go through years of disbelief and sometimes even accusations of child abuse because their doctors aren't clued up enough to pick up on the real problem. The link to the HMSA in an earlier post is an excellent one: these people are most helpful and full of good advice. Just remember that their members are primarily at the more severe end of the spectrum, so don't be too worried by other people's experiences.