One thing I am not seeing here that helps is PRAISE when the dog potties outside. Verbal praise, cookies, pets, whatever the dog likes. Generally, dogs are highly motivated to please, and if you reward them immediately for doing whatever it is that you want them to do, in this case potty on command outside, that positive reinforcement will help them learn much more quickly. Once they know what on earth it is that you want, they're happy to oblige. This also teaches them to go on command, even if they don't really 'have' to go at the moment. Having a dog that will do so is VERY handy on trips, etc. Some dogs, especially if they're new to the household, are too anxious and worried about being locked outside to actually go out into the yard to potty and just sit by the door wanting back in when they're new and in training too.
With a young adult dog, they can physically hold their bladder for 8 hours give or take, but you have to teach them that is what you want before you can even begin to expect it. When not directly supervised in the house (as in, eyes-on-the-dog), the dog should be confined either with a leash, a kennel, or a pen just like a puppy. I also recommend picking up their water bowl overnight and feeding/last water at least an hour before bed. Take her out right when she wakes up and when you get home, right before bed, and 15-60 minutes or so after eating or playing as those are the times dogs tend to need to go anyway, so you can 'catch her in the act' and reward her for doing the right thing. Other than that, every hour or three should be fine if she's actually going when you take her out.
If they do go in the house, that is you, the human, at fault for giving them a chance to mess up. I have retrained more than one dog that had been disciplined (nose in poop, a stern talking to, etc, what counts as punishment varies depending on the sensitivity of the dog) for messing in the house, and the only thing they had learned was that it was bad to potty where a human would see them, so they got better at sneaking off to potty. If you catch them in the act, immediately take them outside of course. If they pottied a half hour ago, they're not going to connect that with getting kicked outside for "punishment." All they know is "human saw a mess, I got punished, best not mess where humans will find it."
People are good at saying "No, don't do that" with dogs, but not nearly as good at the "Yes! Good dog! Keep doing that" (in this case, when they potty outside) part of the equation. Yes, this does mean that you need to go outside with the dog while you're training them. I have never had any of my foster dogs take more than two weeks to 100% potty train this way unless there was an underlying medical issue (incontinence, infection, cushings, etc). Even dogs who were surrendered to the shelter for house-soiling. Usually they would be 75% reliable in 3-4 days.
ETA: I would love pictures too! Heelers are one of my favorite breeds!