What to do make a 7 year old girl feel less homesick?

Some of my friends came over yesterday to sleepover and my friend, Kiera, who is my age brought her little 7 year old sister, Kennedy. They usually ALWAYS come over but this time Kennedy wanted her mom to come and pick her up early but she wouldn’t. So now I think she feels homesick because she has been crying and stuff. And I don’t want Kiera to leave but if Kennedy gets picked up she will have to. So how can I make her feel less homesick and they might actually get to sleep over again.