In A Doll's House, Dr. Rank tells Nora that he loves her. This confession makes Nora re-think her plan to make her own confession to Dr. Rank.
Before his confession of his love for Nora, Dr. Rank was a good friend who might be counted on to keep a secret and to help. After his confession he is no longer in such a simple position, relating to Nora, and has actually set himself in a position of weakness.
If Nora were to ask Dr. Rank for help after his confession, she would have been taking advantage of his weakness, of his honesty, and taking advantage of his feelings for her.
She had wanted to ask for the help of a friend, an equal, but after the confession decides against asking for help from someone who is already emotionally indebted to her, in a manner of speaking.
Also, if Nora asks Dr. Rank for help after his confession the two of them would enter into a secret pact charged with too much meaning to be easily explained or dealt with. Once love becomes part of the bargain, the potential for a cut-and-dry (although secret) agreement is eliminated. Love promises a messy secret and a potentially dangerous situation if Torvald were to find out.