I’m so sorry to hear this. I really thought the fabulous new cage would change her behavior. There isn’t anything you haven’t tried.
I understand the frustration of rehoming a large snake. I had a 12’ albino burm that I’d had for 16 years. I had been trying to rehome her for about a year. I was only l only considering very experienced keepers because she did not have the typical laid back burm personality. She was an extremely agressive feeder (lunge out of the cage) and was often difficult to handle...hissy, irritable, and prone to striking out when she didn’t want to be bothered. When my other half passed away in April of this year, I reached out again to every rescue group and local zoo up to a 2-3 hour drive from home. In the end I had to make the choice to put her down. I couldn’t safely take her out or feed her alone, and the few friends I have that are okay with most of my collection wouldn’t get near her because if her size and temperament. Ultimately it came down to I couldn’t let her really hurt someone or worse. It is still one of the hardest decisions I have ever made.