"Special needs" is an umbrella term that encompasses a vast range of needs and abilities, including difficulties in learning and physiological conditions, either singly or in combination with one another.
It is impossible to answer all such diverse requirements here; however, there are a few pointers that will get you started.
1. Be realistic. Although most children with special needs have the potential to enjoy an improved sleep pattern, it often takes longer than for their peers without special needs.
2. Be prepared. As it is likely to take even more perseverance to encourage a special needs child to sleep better, you will need even greater resolve. If it is appropriate, try to arrange support from friends and family, so that you can pace yourself and have the occasional break.
3. See the complete picture. To give your child the best chance of achieving better sleep patterns, it is important that her diverse needs are taken into account. Most sleep training focuses on behavioural and cognitive techniques, but if, for example, she has Downs Syndrome it may be that she has respiratory problems that are interfering with her sleep - for many children with Downs Syndrome, removing their tonsils alleviates breathing difficulties. Similarly, it is important to reflect upon the needs of the wider family.
4. Mix and match. Although your child has unique needs that have to be responded to individually, you can adopt some of the basics of sleep training. For example, establishing a consistent routine will help her to understand that certain things happen in a set order at certain times of the day, and sleep is one of these. Similarly, although no one technique may be right for your child, there may be elements you can use from each that will match her needs and help her to sleep better.
5. Get help. You don't have to tackle this alone. Your health visitor will be keen to advise you, or you can consult the paediatric department at your local hospital, or visit a specialist sleep clinic. You may also have access to one of the charities that offers sleep counselling, advice and support to families of special-needs children with sleep problems.