Mare Do Well attempting to be romantic by taking Rainbow Dash to see a sunrise.
When Rainbow Dash has her wings broken, Mare Do Well feels so guilty that she begins avoiding her, only for Rainbow Dash to realize that she actually misses her. Later, Dash runs into her completely by accident and actually tries to comfort her when Mare Do Well begins crying.
Rainbow Dash and Mare Do Well falling asleep together under Mare Do Well's cloak. Made even better by how neither of them wanted to move upon waking, both of them thinking that the other was still asleep.
The Reveal and its immediate aftermath; even though Rainbow is quite justifiably angry with Pinkie Pie, she's determined to find some way to make things work out. She got the Element of Loyalty for a reason.
The moment just before the reveal, when Mare Do Well is unmasked but Rainbow Dash still has her eyes closed and can't stop kissing her. I don't know if heartwarming is precisely the right word, but it's certainly very emotionally intense.
Rainbow Dash doesn't care who's under that mask; she knows she'll love her no matter what. So yeah, it qualifies.
The chapter can be perfectly summed up by this portion:
So, no, one night wasn't enough to fully repair the damage that had been done. But there was no time limit, after all — no rule saying they only had one night. They were friends and lived in the same village, seeing each other nearly every day. They had as many nights as they wanted to find their way. If it took a thousand, so be it.