She is a beauty!
I'd definately first try and find her owners, it's very possible that she was dumped and if that is the case no one will claim her. If you are afraid someone will say she's theirs when she's not, don't let them see her until they describe her to you.
Not wearing a collar may or may not mean anything, it may have slipped off, or the owners may leave it off for safety reason. I use to always keep collars on my dogs, until Iris (dane) joined the family, she's a major neck/collar grabber and I don't want to risk someone getting strangled. Mine are kept in a fenced yard and spend the majority of their time inside, but if they ever got lost I'd really be upset if someone found them and pretended not to have them. Even without the neck pulling my little dog is hairless and so far all collars I have tried irritate her neck if left on for more then a day, so she only wears one when I take her with me.
Sorry I know I'm rambling, I just hate to hear people say don't bother looking for an owner. I lost a dog a few years ago, never found what happened to him, my guess is either something happened to him (like he was killed), or someone picked him up, and since we were never able to find any signs of him (blood, a body, hair, etc.) I can't help but think he was picked up. I did everything I know to find him and never found a clue. I'd hate to think someone had him and just desided they wanted to keep him.
In your case I'm going to guess this poor girl is a dumpy, but it doesn't hurt to cover your basis by atleast getting the word out that you have her. I'd give it a week and then assume she's your's!
Here's a pic of our aussie mix (hard to believe her mom was a hound!), Storm,
She was a rescue, along with her 5 sisters when they were puppies, can you believe no one wanted her? But she's great, very loving, especially loves children. Let's my baby goats crawl all over her. But she does have one major flaw, she kills chickens. Completely my fault, I trusted her to fast. I can let her out and around them, and as long as I'm with her their safe, I just can't leave her unsupervised.
I know I'm rambling again, good luck with your new girl! Have you picked a name yet?