Tip watching a video of herself and her mom twice, once in her room before leaving, and again when Oh leaves her in Slushcious to swim in the ocean.
And the conversation between her and Oh that follows that second scene.
Pig rushing inside at the sound of Lucy's voice, only for Tip to console the cat that it's just a video, makes the first instance all the more touching. Tip's plainly being strong for Pig because it helps her stay strong herself.
The reunion between Tip and Lucy.
Before that, Tip fruitlessly searches through the hundreds of resettled humans for Lucy, becoming more and more discouraged. She shows a few people a picture of her mom on her cellphone, but none of them recognize her ... and then the phone's battery dies. Eventually, she gives up, and sits in the empty "Ask a Boov" booth, utterly broken.
She may be a brave girl, but she's still just a little girl looking for her mom.
Tip thinking that Oh got crushed under the Gorg mothership, not to mention the stiff upper lip smile Oh had when he was looking at Tip moments before. Thankfully he wasn't.
Oh becoming utterly crushed when not a single Boov came to his housewarming party.
Oh admitting to Tip that he knows what his name means and that he doesn't have any friends.
Lucy desperately pleading with a Boov to help her find her daughter. At this point, she barely even cares about the invasion or the fact that a new race now rules the Earth. She just wants to see her little girl again.