Sayori is super bubbly! I think the distinction between her and Monika is the sincerity behind this cheerfulness. She can be a little more teasing, fun, and light-hearted, because she wants to promote real joy rather than simply maintain the facade of harmony. That said, she is also frequently put down by others, and needs to be able to convey the feeling of a kid being caught doing something wrong. Remember to try multiple takes/inflections for each sample line-- show your range and be creative!