You tell Moonflower that it's been fun, but you should get going. Having borrowed a cart to mine some gems for a friend, you don't want her to worry by being gone for too long.

Moonflower: "Awww! But I wanted to hang out some more...

Ooh, I know! I got this cap now! Maybe I can go with you? I bet I could totally help you out with my plant knowledge or somethin'! Please? I won't be any trouble, I super promise!"