If the daughter is considered "permanently and totally disabled", yes, it sounds like the mother can claim the daughter.

https://www.irs.gov/publications/p501#en_US_2018_publink1000220897

However, Asperger's syndrome and ADHD would not necessarily mean the child is "permanently and totally disabled".  If the child collects Social Security Disability, that would probably be a solid way to determine that the child qualifies.  If the child does not qualify for Social Security Disability, that does not necessarily mean she would not qualify as "permanently and totally disabled", but you would want to solidly document that situation, perhaps including doctors notes that "she can't engage in any substantial gainful activity".