You can love her and need help.
Those two things can be true at the same time. A tired day, a shorter temper, or a wish for an afternoon to yourself does not measure how much you care.
Try naming what the promise really meant.
Was it that she would be listened to? That she would be treated kindly? That you would keep showing up? Those things can remain true when someone else helps with part of her care.
Ask a smaller question.
Instead of “Am I ready to hand everything over?”, try “What is one thing someone else could help with this week?” You don’t have to choose a forever plan to explore a little support.
Include her in the meaning of the promise.
You might say: “I want to keep being here for you. I also want us to have time together that isn’t only about what needs doing. Can we talk about one thing that would make this easier for both of us?”