Concerned about adopting a new dog due to past vet experiences

I wanted to ask advice on adopting another dog in the near future. I am mostly concerned about my past vet history with my current dog and how it may be perceived by rescues due to mine and my family's errors.

I currently have one dog, a senior chihuahua, whom I got from my grandma when I was around 8 or 9. My grandma was what I now know as a backyard breeder. I am unsure of what health testing, if any, she did, but I know she gave her own vaccines and medications to the dogs and rarely took them to the vet unless absolutely necessary. My parents inherited this state of mind and do not take their dogs to the vet often, if at all. Their dogs rarely get vaccines (only really rabies). They also got their dogs from backyard breeders and from friends and those dogs had medical issues that were not addressed.

As a result of this history and upbringing, I have had to relearn a lot of beliefs about vets and dog care that probably looks very bad on paper. I have been trying to educate myself on what proper dog care looks like and how to best support my dog in the end of her life.

Over the last two or so years I have taken full control of my dog's health and wellness, including vaccines, trips to the vet, etc. I had to inform our vet of the deaths of several dogs they had on record that my parents had not updated as well as the existence of another that never went to vet all the way to his death. I have kept my girl vaccinated according to the recommendations of my vet for her age (again really only rabies, as she does not spend time around other dogs and has not been boarded or anything). She has received vaccines in the past but they were from our local shelter or purchased and administered by my grandma, and unfortunately we do not have her records anymore due to a housefire.

The worst thing I've done to my girl was not getting her spayed. There was no reason why she was not spayed - she has never been pregnant nor did we have any intentions or her having puppies. My parents did not get her spayed while I was growing up and by the time she came into my care she was already 12 or 13 and I did not want to stress her or risk complications by putting her under anesthesia. I regretted this several months ago when she developed a pyometra. Luckily, we caught it quick and she took the surgery well initially. However, during the surgery the vet found several lumps they believe to be cancer, likely also caused by not getting her spayed earlier. Due to her age, the vet recommended several medications (that she is taking) to preserve her quality of life until it is time for her to pass (which she will do by my side).

I feel horrible about not being able to care for her better or sooner. I love my girl more than anything and I am doing the best I can to support her now that I know better. She receives the best food I can provide her (she loves Royal Canin), she sleeps with me, she is crate trained and potty trained, and we go on walks together through the neighborhood every day. Dogs are the only children I will ever have and I intend to treat them that way.

As she is getting closer to the end of her life, I am looking to potentially adopt a new dog in the future (preferably another chihuahua or small dog) to help me through her passing. However, I know that many rescues and shelters require a vet reference, and I am worried about how this will impact my chances of being able to adopt. Like I said, I am actively working to re-educate myself on the medical needs of dogs and how to be the best dog owner possible. I even volunteer at my local shelter so I can have a better idea on how to treat and interact with dogs that are not her. Is there a good way to communicate this to the rescue organization? Does anyone else have experience with this, or know of resources I can look into? I appreciate any feedback y'all are willing to give. Thank you sincerely.