Hi Eloise73, so....DLA
DLA is a benefit payable to the child, not you, so it is entirely based on her circumstances, although you as her representative will receive the money to do as you see fit with. It is an important distinction, because it answers your questions about your job, etc. The only exception to that is if the child is in residential care (e.g. residential school), when it all gets a bit more complicated.
In answer to your other question, DLA isn't based on diagnosis, but on care needs. So a child who has no additional care needs would not get DLA regardless of their diagnosis.
The Care part of the DLA is split into 3 categories. Basically:
Low Rate Care: 1 hour of 'extra' care per day.
Mid Rate Care: 'Frequent' care throughout the day or care during the night
High Rate Care: Frequent care during the day and at night (20 mins + or more than twice per night)
The mobility part is split into 2 categories:
Low Rate Mobility Over 5 years old
High Rate Mobility Over 3 years old and unable to walk, virtually unable to walk, or Severely mentally impaired with severe behavioural problems and entitled to High Rate Care.
The Cerebra guide to claiming DLA is excellent, and can be downloaded from the cerebra website.