S.H.
you might want to find a support group for her, the kind that is specifically for children, with these medical issues.
That might help her to see other kids that are like her... thus, making her feel better perhaps. Try asking your local hospital if they know any support groups for her, or do a Google search of it in your area.
Also her age... 9 years old is nowadays considered to be pre-puberty and in fact, some girls this age start puberty at this age... the bodily changes, hormones, mood changes etc.
Does your daughter have any friends?
Or perhaps, nurture any hobbies or interests she has... and if so, maybe she can join a club that does these activities.
Or even a reading group club? Since she seems to like reading. Thereby, assimilating her with people and things that already are in her interest area.
Ultimately, you'd want to ask your Pediatrician... instead of guessing at it and what could be wrong with her.... and/or any "medications" or homeopathic remedies that could help her.
Its most probably a COMBINATION of things that is affecting her: her cerebral palsy/seizures, her sensory issues, her age and it's biological changes, her social life, her sense of being and a child's development of emotions at each age juncture... her sense of self...
With kids, it is often a combination of things that compound how they feel...
Also, see if there is anything wrong or any problems she is encountering at school? With her friends? What do her teachers say? Any problems there? Find out, or see what they suggest.
All the best, just some ideas,
Susan