I feel like I failed as a foster parent

Hi all, I thought coming on here may make me feel better. My boyfriend and I decided to foster a dog about 3 months ago from a local kill shelter. I’ve never fostered and she was on the euthanasia list and I felt inclined to get her. Upon getting her, they sent us home with only a bag of food and a leash (which is fine, my family had a large crate for her.) They did not send her home with a cone, and she is a 75 lb pit bull mix who had just been spayed. Her spay incision was 7 inches long and actually ended up coming undone (her organs and intestines literally were hanging out of her body) so we had to rush her to an emergency vet where they told us this was the fourth case this week where the same thing had happened. It was traumatizing but also made me form a bond with her since she made it out great. I have a 10 year old blue heeler who gets along fine with her, but she is 3 years old and is bigger and always wanting to play. I noticed during Christmas a lot of dogs on the euthanasia list were adopted out, and as I post on social media and send them photos to upload of her - I feel like I am getting no where. They are charging $40 for her to be adopted, but posted today that “all dogs at the shelter who are spayed and neutered will be free to go home today.” I do understand why people need to pay, we shouldn’t just let anyone obtain a dog and if you can’t spend $40 on a pet how can you plan to financially care for one? I just don’t think anyone would pay $40 for a pitbull mix who’s 3 years old and not trained. I guess I just came here because I feel helpless. She’s a beautiful dog and incredibly sweet, but my old dog comes first and I just am lost on what to do. I don’t usually use Reddit but I thought this may be a last resort before I consider returning her. If anyone has any advice on ideas to get her adopted (I post on social media often and take her places frequently) I would appreciate it. It’s been on my mind all day and I’m having an inner battle of taking care of my dog but also helping her. 😭