As a former working mother, I agree with the suggestions that have been given you. Actually, even as a working grandmother, I have to be organized and plan. My grandchildren live out of state, and to ensure that I can take the needed time off to go to their birthdays, I get my leave on the calendar.
I also think that you should start documenting her requests, comments, the accommodations that you do give her, the times that coworkers take up her slack, and any other issues with her work that you have. You may need the documentation in the future.
Persistence is more important than Perfection
Continuous effort - not strength or intelligence - is the key to unlocking our potential. - Winston Churchill