I see. Well, there are usually reasons why an adolescent may hide important and "meaningful" things form parents. Usually, it is because they feel that if they talked they would be blamed or pressurized or not understood. It is very important for you to understand that she has not obviously been happy the last few years as you have thought all along. You need to admit this to yourselves, which can be a hard thing to do as it can elicit feelings of guilt such as "how did I not realize this". To tell her things (and I am not saying that you do, I am using it as an example) such as "but how did this happen, you have always been a happy child" does not help at all because then she feels that you cannot contain her feelings of sadness, desperation, anxiety
, anger or whatever intense feeling led her to cause pain to herself. Dismissing feelings will only lead to further isolation.
Therefore, I would advise that you approached her with sincerity telling her that you feel guilty for not being there for her when she obviously needed you more. Ask her to tell you all her complaints about you whatever those may be. Do not focus on the attempt so much as this is just a symptom of her desperation at the time. So ti would be best to listen to her and encourage her to talk about herself, accepting everything without passing any judgment on her.
If she still denies seeing a therapist, then I would strongly encourage you to see a child therapist//psychologist to receive some more specific advice and guidance. You can explain your views and see what you could improve in your communication with her.
It is a good thing that she told you. This shows that she still believes that you can help her. It is now all about proper handling so she trust you to take her to a therapist. It will take some time but if you try and work on your relationship then she will be able to move on and work on her issues, whether this is bullying
or a traumatic incident.
I hope this helps. Please feel free to share any feedback on these thoughts
All the best