How do you know if your guinea pigs like you?

well one thing is that your guinea pig would not run from you in a cage and would not bite you.

My sister's guinea pig always squeaks when it hears something familiar of my sister. Like, the certain squeaky sound that her door makes. Also when she walks by. Another thing is that Trixi (the guinea pig) chatters or purs when my sis pets her, but only when my sis pets Trixi.