Needs unpicking really.
Where I live, there are long waiting lists for diagnostic assessments (although not 18months), but it seems from your OP that he has diagnoses ? Again, that seems unusual as ADHD isn't diagnosed in 3 yr olds as so many of the symptoms describe toddlers 'normal' behaviour.
So there are two separate issues. They can go on alongside one another though, one does not rely on the other being complete.
There is the responsibility of Health services - who do assessments, provide a diagnosis (or diagnoses, or decide the child doesn't have known condition), and provide 'therapists' - physios, speech and language therapists, occupational therapists - and, sometimes support from specialist nurses or dieticians etc., depending on need.
Then there is the Education side of things. If he is struggling at Pre-school, and is also likely to struggle at school, then the SENCo (Special Educational Needs Co-ordinator) should be supporting him whilst he is in pre-school and his Mum/family in terms of putting plans in place - possibly working towards applying for an assessment for an EHC (Education Health Care) Plan.... this will depend on need.
There are some sleep clinics too.
She needs to go back to whoever has given the diagnosis and get more support with referrals re sleep.
She needs to go back to the Pre-school and ask what they can do.
If he has Aspergers then look up NAS (National Autism Society) - websites and FB. They have parents support groups, they have training courses, chat rooms, FAQs, all sorts of resources and signposting.
She should also go along to her local Children's Centre and see what they have to offer. They all work differently, but even when they can't help directly, they can signpost to someone who can.