Gamora was too young to remember all the details of the first time she met Nebula. She can't remember how old they were or where they were or everything said. She remembers that she was doing agility and flexibility exercises when one of Thanos's crones glided in. His face is darkened with a fog now, but she still feels cold thinking about his hand on Nebula's shoulder.
He instructed her to lead the girl through stretching while he made "preparations," then he sputtered away like steam.
Gamora remembers guiding Nebula through touching her toes, lunging, and standing on one foot. She remembers Nebula getting bored and sitting on the trampoline in protest.
"No!"
"C'mon, it's just half-moon pose!"
"No!" she insisted and curled on her side.
Gamora resolved things the only way she knew: lashing out. She jumped on the trampoline and sent Nebula to the air. When she came back down, she laughed gleefully, "Again! Again!" She scuttled to the center and sat cross-legged, ready for launch. How could Gamora say no to that?
They spent much of the day testing how many flips they could do. They spent much of their time together either fighting or playing, just like lapdogs.