With respect to Emma in reference to her being the key to breaking the curse. Look at her in the same way as that key ring with all of those skeleton keys. Those keys opens up all doors in SB. The most used symbols are keys. Almost every episode there is a key symbol whether it be an actual key or not. Emma is the master key to breaking the curse. She like each key unlocks a door. Emma unlocks certain things in different people and places.
1. The clock started to move.
2. Every stop light when she arrived in town was blinking red. As the episodes continue some of those lights stopped blinking red and started to work or blink green.
3. Jefferson was free to exit and enter his house.
4, After she kissed Graham he got his epiphany of his past life.
5. Emma partially helped Ashley and Sean.
6. She reunited Hansel and Gretel with their Dad but still a partial.
7. It seems David/ Charming is starting remember and perhaps Kathryn/ Abigail is in the same boat.
8. Emma has kept Mary Margaret from being lonely as herself too.