When Paul's wife is chatting motherly with Sophie while helping her get of her wet clothes (due to her having two broken arms), Sophie suddenly hugs her. Hell, Sophie always managed to warm my heart.
Even though Walter isn't thrilled about it, it is very heartwarming to see his daughter watch over her depressed father.
In her last episode, April tells Paul that he finally has a review on his website. It's from Sophie who writes that Paul saved her life.
When Paul reveals to Mia that he kept a tape of her on the piano as a child and plays it for her, she responds with a little girl's grin that attaches towing cables to the heart and flings it into the distance.