Let's start with the timeline for "Daleks In Manhattan"/"Evolution Of The Daleks", because that ties in with a question that was raised somewhere online in the last few days: How is it that the TARDIS always knows where the Doctor needs to be?
Since the TARDIS is alive, I figure its consciousness must somehow be tied into the time-stream. It can detect disturbances in it caused by others and knows that its own master would probably be keen to investigate those.
So it landed in New York City on November 1st, 1930, because it was the focal point for several other time travel trips. 1930 was the year in which Dr. Leonard H. McCoy saved the life of Edith Keeler after he went through the Guardian's portal. Her survival caused the annihilation of the future in which Starfleet came to pass.
Therefore, Captain James T. Kirk and Mr. Spock had to go back in time to prevent McCoy from altering the past. (This happened in one of the most popular episodes of 'Star Trek', "City On The Edge Of Forever".)
Although we only know that the year is 1930, it appears to be chilly enough that people need coats; yet it's not wintery. There's also just this sense of the season fading, rather than the promise of a spring awakening, so it could be in the late fall.
And it would be better for the late fall with regards to the mention of Kirk and Miss Keeler going to see a Clark Gable movie. In the real world, Gable didn't headline a picture until 1934; didn't get a prominent role until 1931. But that's the real world, things are obviously different in Toobworld. So if the movie is situated closer to 1931, it brings some alignment to the discrepancies between both worlds when it comes to Clark Gable.
Such an extreme alteration to the timeline must have been felt by the TARDIS, but by the time it reached New York City they had more important things to investigate.
That brings me to the second reason why the TARDIS always brings the Doctor to where he's most needed. Those same psychic senses displayed by his conveyance might be expansive enough to sense dangers anywhere in the universe, even if it has no connection to timeline disruptions.
In many of the Doctor's adventures, I would say it's a combination of those senses that come into play when the TARDIS locks onto a destination. So although the TARDIS brought them to 1930 Manhattan with the intention of getting the Doctor to prevent the seismic change to the timeline, the threat from the Daleks was far greater.
If I remember correctly, at the end of "Evolution Of The Daleks" there was room between the scene where Laszlo and Tallulah are accepted into Hooverville, and the scene where Martha and the Doctor have returned to the TARDIS at Liberty Island.
So could it be they still had time to squeeze in a visit to the Twenty-First Street Mission, albeit too late to get involved in the fate of Edith Keeler? For all we know, the Doctor and Martha were there on the street as observers, knowing they could not risk getting involved. (Not that it mattered, ultimately - Kirk and Spock were successful in preventing McCoy from saving Miss Keeler's life.)
The harsh cruelty of Edith Keeler's fate for the sake of the future may have disturbed Martha and made her hope all the more fervently for the success in the relationship of Laszlo and Tallulah. This would be a good reason why it was still on her mind as they prepared to leave, even though the events at the Mission might have been more recent in her memories.