We just recentley let our cat go outside, now she is acting strange, What may be wrong with her?

She is a Calico, very energetic and a bit too playful and very rough. Recentley she has had this urge to go roam around outside. We let her outside one day and she refused to come back into the house. She was outside for about 5 hours. We kept an eye on her for the most part, but when we finally got her into the house, she started to hiss at me and ran into a corner and has been there ever since. We have no idea what is wrong with her, shes been acting very strange, almost depressed. She didnt seem scared what so ever.