So maybe try what Henry&Friends suggested. Leave a window open and it might come into your house.
that’s a last resort option though— I wouldn’t want one of those things flipping out all over my house!
As long as it isn’t too cold out, you can toss it some food in the morning and it’ll forage for food & roost somewhere at night. Something might’ve happened to its flock are we sure it’s a guinea hen? It’s really hard to sex them, the best way to sex them is to listen to their screaming, I think a hen does one syllable and a cock does two.