Thanks for writing in.
Your daughter aged 15 years, is suffering from a mastoiditis
. This is a chronic infective condition affecting the petrous part of temporal bone
. She is lucky not to have any involvement into the brain.
This problem can usually be treated with medications and may need a complete ear examination.
Coming to your journey by flight, she will not experience any adverse problem during flight. However slight pain may be there due to cabin pressure variations in flight. This is an acceptable situation.
Hope this helps.