Bless you for adopting Maggie, but I am sorry to hear about the dental issues. I totally understand your frustration with people not properly caring for their animals. I can tell you that when our Angel was around 14, she developed some horrendous breath and the vet said to remove the teeth (2) was $3500.00 because the roots go clear up under the eye. Hubby did not want to subject Angel to that because of her age, plus he doesn't believe in spending that kind of money on a dog. PLEASE don't kill me, this was HIS dog and I couldn't change his mind. But just an example on how people view their animals.
Just to reassure everyone, I plan to do yearly (or more frequent if necessary) dental cleanings on Annie to avoid this.
I am not very experienced in these things, so hopefully more posters will offer you better advice, but maybe you can work something out with your vet?