It is unclear from your post if this cat was a newborn when you first discovered her. If so, you stand a good chance of being able to tame her down. Even if not, she still will need to go to a vet to be spayed, and then released back into the yard. Most animal agencies rent or lend (with a refundable deposit) humane traps that you could set out for her. If you do decide to attempt to tame her and keep her inside, she'll feel safer if you can keep her in a crate or a small room by herself away from the dogs, other cats, and noise of the household. There are many old posts that give excellent tips on taming feral cats - Jasper's mom had a very successful attempt last month. I am at work on my lunch hour so I don't have time to search and link the old posts or to explain how you can find them, so if you're not a bulletin board pro and want to find these old posts, anyone here can help you with it, just ask. And, bless you for wanting to help this little girl.