There may be an older carers project in her area for older parents of people with learning disabilities who she could contact. I used to run one, and they are concerned with future planning for the family, eg. where the person will live when mum and dad are no longer around or unable to care. What area is your friend in? If it's Yorkshire I might be able to point you in the right direction or is your MN name a red herring?
A useful website is sibs.org.uk, sibs provides support for children and adults who have siblings with special needs. They hold workshops for siblings like your friend around the country from time to time.
The Mencap website has some useful information on types of housing and older carers. There is also a Housing Options website. She might find out about local support groups from her local carers centre though.