So when Sunlight and Autumn first meet, because of Forest and Autumn becoming roommates, Sunlight doesn’t know anything about Autumn, but everypony in Withervale knows who Sunlight is including Autumn. Sunlight is severely caught off guard when Autumn starts to put on very clever flirting and pickup lines.
 
Sunlight has no idea what to do in response. It doesn’t help that Autumn is an expert at sleeping with other mares, while Sunlight still has her virginity.
 
Also their size ratio here is off, Autumn is not this much bigger than Sunlight. Also Autumn nicknames Sunlight Sunnybutt.