dear daughter is a Club Rainbow member Useful Organisations, Special Schools and Therapies ... scroll to CRS
I had attended 1 overseas trip with CRS - Star Cruise to Penang/Phuket. Since this is a big event, there are doctors and volunteers to take care of children with special needs. Maybe can try Star Cruise?
Going alone means you plan and travel all by yrself. Even thru agt, there could be some restrictions .... depends on yr luck to get a good organiser. Would think a super light weight stroller with at least 1 recline position for yr gal is important. Since on wheels, crowded places and countryside where climbing is a taste of endurance and could ruin yr holiday mood. Sarong for long journey ... carry a ±15kg child is no joke!
Also, you need to consider medical supplies ... eg equipment or medication.
I think Australia .... those western countries r more friendly to ppl with special needs.