What a story! It sounds like a really poorly run home! I don't know if there are any other places where your mother might be better cared for?
I worked in care for years. Between inept management, institutionalised carers (that put routine over good practice), and (no offense) demanding relatives, it is often impossible to even take care of individuals basic needs on a daily basis, never mind going over and above.
I am sorry to be blunt, but this is a HUGE societal problem, that your complaints are unlikely to fix any time soon, unfortunately.
I would really suggest focusing on what you can do immediately for your mother, especially if she isn't getting regular meals!
If you can't take her out of there (and even if you do), I would really recommend ignoring the management's policy (or at least recognising it's limits), and talking to the regular staff that see your mother every day, and that cook for her, if possible.
Could she have her own calendar, or a communication book in her room, where you can write in the dates of your visits? That way a conscientious staff member might take the time to directly inform the kitchen staff.
Wishing you and your mother well, and kudos to you for going up the ladder with this issue!
I can tell you that I had to leave the profession because of personal stresses, but also because I strived to promote best practice, and that is a sure fire way of making enemies in lots of these establishments, unfortunately