It could be something like hypermobility, or it could be just she tells you all the time.
I am certain that dd1 and dd2 have similar amounts of illness/injuries other than dd2's migraines.
But in a typical week, dd2 will have had told me about pain in her: knee, back, arm, ankle, chin, ear, throat and little finger.
Dd1 might have said "ouch" quietly and then said "no it's fine" when I asked what's wrong.
The result is that for dd2, I'm telling her to get to bed, it'll be better in the morning (and 99.9% of the time it is) when I'd have been jumping in the car and going down to A&E with half the fuss with dd1.
It's just different personalities.
Dd1 doesn't like a fuss made and tends to keep quiet unless it's unbearable. She will avoid seeing the doctor if possible-she's been twice in the last 8 years, and one of those was a routine check.
Dd2 likes to tell you everything and have sympathy and preferably a nice chat with a doctor who also gives her a sympathy.