Adhd can range in severity yes. I'm an SEN teacher but I also have it myself, well into my 30s.
It caused me absolutely collossal problems at school (to the point I was asked to leave ) and has continuedd to cause issues well into my adult life.
Partly though my work and just growing older I've learned ways to manage it better (but by no means perfectly) and I have always chosen that I wouldn't want to take meds.
My advice would be listen to your daughter (I know you are doing but I mean take her at her word), she's 17 and obviously has a good enough insight into herself to know that she feels a certain way, and that the way she feels is a) potentially different to those around her and b) impacting her negatively. If she feels like this is something that she wishes to explore further then I would do that. You can speak to your GP or, as others have said the Senco at school . If she doesn't feel she wants to contact her GP j wouldn't push it but just allow her the time to think about going and doing so when she wishes.
@Agirlcalled being a hard worker is nothing to do with having adhd or not. I have a degree and a teaching degree - I am an extremely hard worker - adhd has no bearing on how hard someone wants to work, but it does stand in the way. To get those qualifications I have struggled so so much, as I said I was asked to leave my school for a period of time as my behaviour was so violent and uncontrollable, and even when at uni, I was by and large unable tk attend lectures and had to catch up on all my work with tutors afterwards, as even in my 20s I was still extremely disruptive and was asked to leave most lectures I attended (to the point we agreed I would stop going and I would have to access the content another way). As. 20 something, being told that despite the fact I wanted to be there and I wanted to do the work, that my behaviour was so inappropriate that I was no longer able to attend, was absolutely devastating, and mortifying. But I wanted the qualifications so I had to accept that we would have to do this another way. At work, I am open with my colleagues about the issues I have (of which obviously they understand because we all teach SEN!) but it's still a struggle so, whilst I appreciate your experience with your own child, having adhd absolutely does NOT mean someone cannot be a hard worker.
Sorry that derailed things a little OP as this isn't about me - but I also don't like misconceptions about things and want to put them straight.
I hope that you are able to get some advice - I must warn you that late diagnoses of things like ADHD and ASD are notoriously difficult to get especially more so for adolescent females, so please be persistent (if that's what your daughter wishes ) because I would not be surprised if your concerns are dismissed initially. Unfortunately there is a lot of that and it can be a fight to get the correct diagnosis and support, so if that happens and your DD wishes to continue to seek help, it may be a matter of having to push on and keep going until you get somewhere
Good luck , and a huge well done to your daughter, whatever she chooses / wants to do, because it is not easy, especially as a teenager, to identify that you are feeling a certain way and speaking out. She should be very proud of herself