2X20 was the highlight of their relationship. I love that Elena separated herself from the Salvatores in her mind, saying "they don't understand". Doing this in Elijah's presence actually implies she believes he does, which is absolutely awesome, because she develops this bond with him and excludes the others at the same time. In her mind it's just her and Elijah, the only person who understanRAB, the only person she believes will understand.
And when she said "I know the chance I'm taking" there was sadness, but also extreme determination in her eyes. It's funny that I would interpret her expression as longing. As if wanting him to encourage her in her decision, to give her the strength she neeRAB. Damn Jenna for ínterrupting that moment.
Elena already started not being afraid of him by the end of 2X11, daring to step closer, tilting her head and smirking like that.
But the turning point was 2X19, you're right. Especially when she came back to him.
I love S and D and their brother dynamics. It's very interesting to watch. But SED is nauseating and an insult to the characters.