Many questions! I don't know what you mean by "how did she come to be" so I'm going to put a pin in that one for now (sorry, feel free to clarify in another ask!) but for the other ones: Isabelle likes punk/goth, pastel, and academia type fashion styles; Isabelle and Cy meet weekly at a cafe to hang out, and if they're in the MoodTM they head back to his uni apartment for kink, but they see each other outside of that weekly thing pretty often; and Lynn....

Isabelle has a tendency to expect every woman she meets, especially older women and especially women whose men she's sexually involved with, to loathe her like her mother did. So Lynn's acceptance of her into the dynamic between her and Cy is wonderful for Isabelle, and starts the process of Isabelle like...relaxing into the fact that she can be liked by and have a meaningful (non-romantic in this case) relationship with another woman. She admires the confidence Lynn has come to have by the time she's in her 60s, and often wishes she could be as unashamed of her own scars. She really respects Lynn's wisdom, resilience, and of course her dedication as a submissive to Cy. Lynn is kinda a mother figure to her in a lot of ways.