I know what you are going through, I also had a situation very similar to the one you describe where the cats were not properly cared for and the person was not doing anything to get them adopted. People mean well but they just totally burn out, they run out of money, they get overwhelmed.
I also agree with you that blowing the whistle on this women is more than likely going to get a lot of the cats needlessly euthanized. And once you involve the authorities they will just follow the law. And the law, unfortunately, never does anything good for the cats. And contrary to what everyone thinks, the HSUS and ASPCA also euthanize most of the cats from hoarders. They publicize all their rescues and then they kill the cats and lie.
The best way to manage ithis is to find out who she networks with in the rescue community (and I'm sure she has friends she works with). You will have to get names out of her unless you already know groups that she works with. Then you have to contact the people in those groups and tell them that she needs help.
Then those people need to start calling her and telling her they have empty cages and they have a lot of really good adopters coming in, and that they heard from you that she has X or Y type of cats that a lot of adopters have been looking for. And then those people have to come over to her house or you need to go over to her house and help get those cats ready for transport to the other shelters.
That is normally how it is done compassionately for everyone involved. It has to be done a little bit at first and then more and more.
You have said you cannot get in touch with her. The one thing she needs most is for someone to reach out to her, take her to lunch, get her to trust and talk to you and confide in you. She needs help and support and so do the cats. The only way they will get what they need is from other shelters. And the only way other shelters will help is if her friends in rescue who are affiliated with those shelters know about her situation and if you help to make it possible for them to get the cats.
The only other way it can be done is if you help hire a service to come in and clean the place up, and then help her get a volunteer program going using high school kids who need volunteer service hours for their college applications.
I know I keep saying you have to get involved, but if not you, then who? This is to help the cats, not necessarily her, altho I do feel for her. This is the way to keep the cats from getting killed and also to improve their conditions. Maybe you can bring a friend or some support for yourself. I know you say she isn't letting people in, but she will let you in if you knock on her door and come with food or something to share with her and just be a friend.