Relationship with mom

I have been working on my thoughts on my relationship with my mother for a while now, but I still get triggered very easily by what she says or does (I know it is due to what I make of it). In the past I had a thick book of manual of what she should or shouldn’t do, and I get that I need to use boundaries instead. I have an internal conflict in my mind where I have this fear of her passing one day and I would regret terribly on how I have been treating her while she is alive. This thought stresses me out so much that I keep not being able to set proper boundaries, and would allow her to do things or say things to me that would make me have upsetting thoughts. Like I told her that it is not convenient to come visit in the morning, instead, could she come in the afternoon please. When she refuses, the boundary that I would have set is that then sorry, this time you may not come to visit as it does not work for me. However, because of my fear mentioned above, I ended up choosing to change my plans to fit her, even though I would feel very resentful and bitter. I worry about her anxiety and clinical depression being affected by my refusal. So then I would get super upset and triggered the next time when I talk to her.

I am unable to get out of this cycle in my thoughts and when I put in positive thoughts like:
She loves me the only way she knows how and that’s ok.
She is exactly the way she is meant to be.
I love her no matter what.
the resulting feeling that I have is not a positive one. When I try to put a feeling first in the F line (like caring) and work backwards to a T, I find I can write sentences but I don’t believe them wholeheartedly.

Would love for some thoughts on how I could guide my thoughts!