I echo what @smithforreal said and trust your instincts. She may be going through a growth spurt. Lots of teens go to bed so late (and you don’t know about it) and are tired during the day. I raised 2 children and have overseen 4 grandkids with similar sleep patterns and they are all now normal sleeping young adults. However, to ease your mind, insist on a complete blood panel no matter what your doctor says. That way you can rule out any medical causes. Make sure you get a copy of the results and remember the test is only a guideline. Always watch how the kids are doing in school grade wise and be concerned if grades are going down.
It’s not easy raising teenagers. And they are notorious sleepers….they need to be as they’re still growing. I hope you have a close relationship with your daughter. Even if that is so, you know they won’t tell you everything. Always follow your heart when it comes to your children.