Carmen,
I think it must be a lot harder with children than it is with a partner or spouse. We feel so damn RESPONSIBLE for them, and it feels like we are abandoning them when we leave them to their own choices.
What happens is they promise, we agree, they start changing the agreement, and we get stuck enforcing it. And feel like the big meanie.
I doubt that she is feeling guilty about putting you in this position. All she knows is you are rocking the boat and disrupting her comfortable status quo. She will make promises to get you off her back and then do as she pleases.
She's an adult, it isn't your job to accommodate her choices. I think it's inevitable she is going to be angry and blame you. You have to be very strong and keep coming here and going to Al-Anon for support that you are doing the best thing for you both.
Hugs,