Thanks for posting your query.
There could be many causes for Depression
Chronic conditions like migraine
would cause her depression.
Even females are more pron for depression due to sensitive nature.
She would have Insomnia
, loss of appetite and not interested in surroundings and feeling sad most of the time.
The cause behind her depression in her case would mostly be Migraine since it is also a chronic illness.
Hope I have answered your query.
Wishing you good health.