For which clause?
Student or Learner
Potter was Mrs. Dursley's sister, but they hadn't met for several years;'' The correct time wound't be a simple past?
***** NOT A TEACHER *****
I believe that "hadn't met" is the correct tense.
Mrs. Potter and Mrs. Dursley had a meeting in 1995.
They then had another meeting in 2000.
So we can say: "When Mrs. Potter met her sister in 2000, they had not met for several years."
The past ("did not meet") would not be appropriate.
But look at this sentence:
"After Mrs. Potter met her sister in 2000, they did not meet (again) for several years (maybe in 2005)."
P.S. Don't forget: we are writing these sentences in 2015. So we are describing something that happened in the past.
P.P.S. And when Mrs. Potter met her sister in 2000, maybe she said something like this to her sister: "Oh, I am so happy to see you. We have not met for several years. Let's have a wonderful time during our two-week reunion."
But there's no indication on the book that they have a meet firstly... that's why I think the time is not correct. Does anyone consider that?
If Mrs Potter and Mrs Dursley are sisters (as the first sentence says), it is extremely unlikely that they have not met previously! It is equally possible that two sisters might not meet each other for several years - they are plenty of possible reasons for that.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.