I don’t think you were too soft because I really don’t think reaction has much to do with it. You were right not to react, the last thing that you want is a confused puppy hiding accidents.They really shouldn’t learn where to go based on your reaction, IMO, when they have an internal sense we can take advantage of to teach them instead. I think you just gave her too much freedom too soon, and it is difficult to break the cycle once accidents are happening.
I agree you should do whatever you possibly can to completely remove any traces of urine. Even if you’ve already treated, I would treat again. If she’s having the accidents in the same spot in your hall and it is feasible to replace, repaint, or reseal the affected portion of flooring/baseboards/carpet, I would do it. Just the existence of a pee spot, that seems completely gone but she can sense traces of, is sending her a conflicting message.
I think it will be a long while to re-teach her, but don’t let it overwhelm you. Set up a clear system to supervise or contain her constantly and be methodical in playing and doing your current training with her in every part of your house, including the hallway. Problem solving how to accomplish the supervision and establishing those habits are the hardest parts, but remember you are establishing YOUR new habits, and once you do that it will become easier to follow through long term. Following through over that long period of time is what will shape the habits of your Havanese. When you stop seeing accidents your life will get a lot easier, but don’t give her freedom right away. Slow is good
I can only imagine it’s challenging to restrict her when the other dogs have freedom, but maybe there are creative ways to manage this. Maybe keep the other dogs elsewhere for part of the day as you practice and introduce her to a small ex pen, and then introduce one of the dogs to the room while she’s in it, and go from there based on what needs to be addressed. Or start giving her “nap time” in an ex pen every day and gradually increase the length of time she’s in it, keeping her tethered to you when she’s out.
Hope to hear more about all of your dogs, and see pictures