Susan

Susan is a single mom who raises Chloe and Lucy.

She is a literature teacher whose students include Nichole and Nichole's blonde classmate and Clear Winner.

She teaches at Chloe's high school but Chloe and her friend Valerie aren't initially seen to be in any of her classes.

Nichole estimates she's at most two years older than Chloe at one point, indicating Susan teaches the seniors.

Valerie later comes over to her place for private tutelage, giving Susan the nickname "SuSu" which makes her blush.