OnlyMe, welcome to the board.
I am an 'only' child of a nparent, who is now very senior, still living on her own. She needs me because of her age, and since I have no siblings, I cannot bring myself to just walk away.
I am an only child too and my mother is living in my grandmother's place by herself. I understand that you feel you cannot walk away but that doesn't mean you can't have a life of your own.
However, I have noticed that her manipulations are becoming much, much worse. Therefore, I am always flipping between trying to be true to myself and protect myself on the one hand, while at the same time having to interact with her because she is 'old' and needs my help.
You put the word, old, in quotes. Any reason for that?

I would suggest two things right from the start: 1)
develop and maintain healthy boundaries (mentally, emotionally, physically...whatever is appropriate)
regarding her at all times not just when you are interacting with her. I know this is really challenging. Read books about it and schedule your time so you are not at her mercy. If you get really good at this, all her crapola will
ideally be like water off a duck's back. 2)find a support group in your community of other senior caregivers if one exists.
Therefore I continue to subject myself to more of her cruel comments and lies.
You don't have to *subject* yourself to anything. Don't take her lies and comments seriously. Treat her like you would a 6 year old - these are just suggestions not commands.

She likely has a hidden agenda and is doing what she knows she can get away with me because she
can (ie, if she can hurt you, she will. if she can use you, she will.) I know that boundaries are necessary around my mother and family, nothing they say or do can penetrate that. Having these boundaries intact is my choice because I will not allow her or them to disrespect, belittle, criticize, humiliate or provoke me into an emotional state of mind because I don't like myself that way. This is MY life and she has no control over how I live it....not anymore. What you might need are ideas on how to take care of YOURSELF. If you want to share more, I am listening.
She has no siblings either, so I can't even share the load with anyone, and I just can't walk away.
My mother has a sister but they hate each other and don't talk. Yes, you can walk away...you are choosing
not to because you are a nice person. I suggest taking some of the power back. Don't give her all the power and don't victimize yourself - she might actually want you to victimize yourself because then you would be easier to control and she can get what she wants. It is likely that controlling others to get what she wants is all she has ever known. Maybe she didn't learn how to take responsibility for herself - ever. I dunno. But she is not gonna change now.
Keep reading the threads of this board that *speak* to you. I have learned SO much in the 4 months I have been here.
I was wondering if there was anyone else in the same sort of situation. I would appreciate some 'coping' ideas, because I intend to survive this!
Thanks for starting this thread, OnlyMe. I look forward to hearing more if you are comfortable sharing. And I am glad you have the intention of surviving. Go out and do something nice for yourself today.
p.s. Rght after I clicked on *submit* I felt and still feel such frustration over our situation as only children. OnlyMe, stay beautiful on the inside and don't let her hurt you. Shine your light. If she can't see it, that is her problem. I'm here if you wanna talk some more.
<<<<<<A Big Hug>>>>>>