A dog that followed me home hasnt left. can i keep it?

[Sidney]

My cousin and I were riding horses down the road and a dog(we didn't even notice it until it had been walking behind us for who knows how long) followed us home. That happened yesterday. Anyways, we live out in the country and there are only a few houses the dog could have come from. She is really friendly around me and the people she has met(like my cousin, brother, grandma, and uncle) but she is really skittish about other stuff so im sure she belonged to someone at least at one time, especially since she has a old looking leather collar on(but no info about the owner). Right now, she is on my porch loose so that if she belongs to someone she can go home whenever she wants. However, she seems pretty at home lol. My cousin and I both put several pictures of her on Facebook, Instagram, etc. to see if anyone recognizes her, but no answers yet. If a lot of time passes(I read that about a month is a good amount of time) can I keep her if she sticks around? I know her owners could come back and get her at any time, but I don't see why I couldn't keep her if no one claimed her. What do you think? no rude answers please