I am pretty sure that you are right about her Dad mentioning the cancer affecting her empathy, attitude, reading social cues in Season 1. It makes a lot of sense now that i have been watching the show all the way from the beginning. She seems to get very overwhelmed by things and her anxiety level is very high. I believe that is a factor as far as how she engages with people including family, her dates, etc. i am sympathetic to Shauna and i feel sad that her mom feels so much guilt.
i really believe therapy could help her a lot as far as dealing with her anxiety, feelings of being overwhelmed, frustration, etc. If she doesn't get this sort of help it will be hard for her to be in a relationship, as well as form and maintain friendships. I am rooting for Shauna because i believe she is capable of more than she thinks. Taking small steps and seeing her own progress could be a great thing.