My sister and her son have Aspergers, She is very difficult to deal with and now we know, I wonder how we can deal with this.

Thank you for your inquiry. Aspergers is a neurological disorder which is marked by difficulties in social interactions and communication. Here is some information I found on Ehow.com.

Step 1
Choose your battles wisely. Breaking an obsession or ritual is like running a war campaign. If not planned wisely or if you attempt to fight on many fronts, you're guaranteed to fail. Not only is it time consuming and tiring, it means you can't devote 100% to each particular area. So, if you have a child with a game obsession, a phobia of baths and bedtime troubles, choose only one to deal with. Personally, and I have had that choice, I dealt with the bedtime troubles. Using logic, a sleep deprived child certainly isn't going to deal with behavioral modification in other areas well. Plus, it was having an effect on his overall health. Deal with the worst first!

Step2
When tackling any problem with any child, Aspergers or not, it's always best to remain calm at all times. Children can feed off your anger, frustration and anxiety, so keeping a level head at all times is essential. If you feel a situation is escalating and elevating your blood pressure, take a step back and collect yourself.

Step3
When breaking an obsession or ritual, examine the ways that you may have fed into this. With my son's bedtime activities, I found I was too tired to fight his waking up at 2am. While dealing with this ritual, I ensured I was in bed early myself so I had enough sleep in me to knock his night owl tendencies on the head.
Step4
Communicate with your child to explain the effect that his or her ritual is having on your family as a whole. My son's 2am wakeup calls were affecting me mentally, emotionally and physically, and I told him so. I pulled some research off the Internet about sleep needs and discussed this with him.
Step5
Be prepared for resistance by arming yourself with suggestions and alternatives to your child's behavior. A great way of doing this is by creating a "social story". Carol Gray's Social Stories site is a great resource for parents and educators alike to create books which will modify behavior in children with autistic spectrum disorders.
Step6
Speak to professionals for advice. Contact your paediatrician for recommendations for behavior therapists. Your local parent support groups and national associations, such as the National Autistic Society, will not only provide you support but the information you need to move forward with your child.
http://www.ehow.com/how_2123587_aspergers-syndrome-childs-obsessions-rituals.html

There are also several sites that offers a lot of information regarding dealing with autism.

Autism Speaks is an organization. http://www.autismspeaks.org/navigating/index.php

Associated Content offers great stories with how to deal with autism and that can be found here http://www.associatedcontent.com/article/107995/through_the_eyes_of_a_mother_dealing.html?cat=70.

Autism Society can be found here http://www.autism-society.org/site/PageServer?pagename=life_home.

I hope this helps, patience would be key although, that would be much easier said than done. Good luck, please keep us informed.