Miss Matty going way out her comfort zone to campaign the benefits of the railway to the citizens of Cranford.
William lifting Peggy from the train.
Peggy when she galloped a pony bareback in skirts. It doesn't look like much, but that is quite a feat, and doubly so in skirts and petticoats.
Peggy standing up to her brother. It's a short moment, but after all the crap he's put her through, it's nice to see her scolding her thief of a brother.
Dr. Harrison saving Jem's life by a risky new surgery that avoided him cutting off his arm and ending his livelihood, thus keeping him out of the workhouse.
Mary fixing all the wrongs done by Dr Jack Marshland, Jessie's relationship with Major Gordon and locating the long-lost Peter Jenkyns, just by writing letters with instructions of what should be done.
Miss Jenkyns going to the funeral with Jessie so that she isn't all alone. It is a big deal because she struggles with the society rules, but she's going what is right. The way Jessie and her father appreciates her gesture and effective help is awesome as well, and it seals their friendship.