Why would past Gamora be in this movie?
Because the more recent Gamora was killed by Thanos.
True, but 2014 Gamora was not in the first GotG movie.
Because she didn't go back to her own timeline. The major storyline will probably revolve around the Guardians searching for her.
How did she not get snapped by Tony when he wished all the baddies to disappear? Afterall, she did arrive with all the baddies together. LOL.
She came with Thanos, but she wasn't on his side. All the fighting she does is against Thanos' army.