Ren Allen

"Problem is, that's the
theory. In practice she chooses to spend her time reading or being on
the pc etc rather than doing the bit she has agreed to do. "

Sounds like a lot of stress to me.
Sounds like she isn't "choosing" the chores at all, but saying what
Mom wants to hear. You won't get total honesty (she probably hates
chores) until you relax.
It's funny, because everyone imagines in a house of freedom, that
the kids are just ignoring the Parents needs and making messes
everywhere...that isn't the truth.
My kids have different priorities than I do, if I saw their lack of
help as robbing MY freedom and time, then I would resent it more.
If I see their messes as them being busy with their interests and
more involved with other things than house cleaning (good for them)
it changes my attitude and I can ask for help without a bunch of
baggage attached.

As to the food restrictions, it sounds like your child has zero self
control...that's caused by controlling their food intake for them.
It will take a long time for her to begin listening to her body
again and make true choices rather than act out of neediness or lack.
If she's wanting you to control it again, that's a sign of someone
unable to make their own decisions. Better she re-learn how to make
her own food choices now, rather than as an adult.
Instead of leaving her to fend for herself (scary when someone has
been controlling you) why don't you try saying "yes" more and more?
Eventually, she will be making her own food choices and not feeling
so needy.

Ren