The second time Martha is jealous of Rose, the Doctor takes her to New New York. Standing next to him in the dark under-city, it's only natural for her to wish she could be up in the open air of the planet. But Martha is starting to realize that her jealousy stretches beyond that. She knows that the Doctor loved Rose, knows that he's still getting over loosing her, knows that going back to the places they had their adventures is part of his grieving process. She respects his right to mourn. But must she be a part of that?
Sometimes, no matter how selfish she thinks it makes her, Martha wishes she had been first. She could have her own time with a Doctor who was not yet burdened with the pain of loosing Rose. She doesn't voice her thoughts to him, though. She mutters about rebounds and moves on. But privately, she thinks that if she had been here before Rose, the Doctor would appreciate her a thousand times more.