Final answer:
Lauren (Alyssa)'s statement is a declarative speech act as it expresses a statement of fact or belief, rather than asking a question, giving a command, or showing strong emotion.
Step-by-step explanation:
The type of speech act expressed by Lauren (Alyssa) in the dialogue is a declarative sentence. This is identified by the fact that Lauren is making a statement of fact or belief, affirming that Lilli/Abby will indeed do something. Unlike interrogative sentences, which ask a question, imperative sentences, which give commands, or exclamatory sentences, which express strong emotion, a declarative sentence simply provides information or states a position.