The stuff with Dylan starts before she goes to the gym with Patricia, she's already overheard Dylan and Sam calling her a milf, and then she has the guitar and cello lesson with Sam and Ellie already told her mom that she thinks she's hot, that and the rubbing suntan lotion on Ellies back with untied top and then rubbing on her butt, if you take those choices.
There was nothing in her conversation with Patricia at the gym that would make her think that it would be OK to flirt with her son, daughter and neighbours kid, and Patricia only told her she lets her trainer grope now and then, nothing more.
I think Sophia's mind is wandering because of the lack of sex in her marriage and things keep happening to her that has nothing to do with her sister, like the movers catching her in her opened robe after already catching her in her nightie when she answered the door, plus the guy seeing all her underwear on the 1st day when they dropped the box. When she visits the school, it's her choice at that stage whether to allow the headmaster to 'hug' her. There's quite a bit that happens before she even goes to the gym with Patricia.
I just don't see Patricia as a major role in Sophia's corruption.