Emma is demonstrating the recency effect.
The recency effect is one of the two effects embodied in the so-called serial position effect. This effect describes how people tend to remember better the first (primacy effect) and the last elements in a series (recency effect), when this person is asked to recall the list.
In this case, Emma only remembers the last people she met out of a long sucession of different people along the party. Therefore, this is an example of the recency effect.
