How did nelly know that things were not going well for isabella at wuthering heights? answers?

In Emily Bronte's Wuthering Heights, Nelly knows that things were not going well for Isabella at Wuthering Heights because she received a letter containing the news. Six weeks after she goes away, Isabella sends a letter to Edgar, declaring her wedding and pleading forgiveness. He does not reply. Afterward, a distressed Isabella sends a letter to Nelly, doubtful on the kindness of Heathcliff. She told Nelly that they are living at Wuthering Heights and she pleads for a visit. She also tells her experiences at Wuthering Heights. Isabella meet Joseph, Hareton, Joseph, and Hindley: All are bad-mannered and hard-hearted. She recognizes her fault but also recognizes that it is too late.