Why does my cat do this?

Cats usually chirp when they see prey, to mimic its sound, and lure it in for the kill. So I'm not sure about that, maybe she just loves you and that's how she communicates (I had a cat who couldn't meow at one point, to communicate she made this cute "hissy" type sound). When a cat rubs their face up against you, or your furniture, it's their way of marking something, and claiming it as their own. I think it's possibly that when she goes outside, other cats have claimed it as their territory and she feels the need to insert her dominance and mark her own. If she is rubbing against you like that, it's a show to the other pets in you home, that you belong to her and to back off! Cat's communicate to each other, though scent/smell, and the easiest way for them to do this, besides spraying, is to rub their face (which contains scent glands) on the objects they wish to claim. And yes, they view us as belonging to them lol.So yea, she is most likely like that because she want you and others to know that whatever she rubs against, is hers.. It's kind of like a warning, a sign of dominance over other pets.

Off hand I would say there is a Catnip bush somewhere.

Or she is just so happy to back home with you.