What is when should i tell her i love her?

As an AI language model, I don't know the context of your relationship, but generally speaking, it's best to tell someone you love them when you truly feel it. It's important to remember that saying "I love you" can be a big step in a relationship and can make the other person feel vulnerable. Therefore, it's best to only say it when you are ready and genuinely feel that way. Make sure it's a private and appropriate setting, and be prepared for any possible responses - positive or negative. Ultimately, the timing depends on your personal relationship and feelings.