I hope I can help. Please remain open minded as to my thoughts.
I totally understand your situation as my mother now 88yo is like your Grandmother in so many ways. One problem you face is that it isnt illegal to act like she is acting in terms of the law. People are free to manipulate, gossip and verbally abuse and they are not breaking any laws, but as soon as you break her property it is breaking the law with something like "malicious damage". So if she made a complaint to the police you could be in trouble- that Goldilocks is what you want to avoid.
If you feel you need a break remember that in many family feuds people often get back together down the track, things change and this could occur. So making things worse right now isnt wise. What is wise is to remove yourself from her life as you see fit and inform your parents and any other person associated with her that you do not want to discuss her in any way if possible. Now people are free to mention her in conversation but in terms of discussing you and her to repair it or the events when you dont wish to- off limits and kindly inform them you dont wish to chat about it.
I found that when my sister and I severed our relationship with our mother 10 years ago, we felt free and alive. We no longer had this person trying to destroy our lifestyle. Xmas over the last 10 years has been perfect with love and care and celebration, before then every xmas was a disaster. Even my first wedding was ruined by my mother. You mentioned jealousy, that is an accurate word for some of these domineering frustrated people.
So my suggestion is, it is your decision to live your life without toxicity, but if you do leave it get on with your life and dont dwell on it. Any reaction from you in the future about her wont help.
Oh, by the way, I would replace the pot plants. There is right and wrong and if we do the wrong thing we should rectify it. Put new ones on her front verandah at night and walk away.
Below is a few threads that will clarify things a little. They are from my experiences so may now refer to your grandmother particularly. You just need to read the first post of each.