R.J.
I would talk with her about introducing new foods... since it's an allergy concern. One thing my mum did / does when watching my son is give me the daily report of everything he's eaten. That way I knew if there were any "new" foods, since she really could have no idea what he'd already had. I also had a list of "please don't" foods. Sometimes that list was summarily ignored (sigh... grandmothers)... but most of the time it wasn't. ANYHOW the list of everything he'd eaten every day kept us on the same page. I mean, she'd probably have a good idea that he wouldn't have had foie gras... but would have no idea if he hadn't had more common things. Anyhow... if I found a new food on the list... she'd stick with 'old favorites' (aka things we both knew he'd already eaten) for the next several days.
Babies (except in extraordinarily rare cases of neurological disorders) don't have "bad habits" about eating. They eat when they're hungry until they're full. They don't overeat. So you don't have to worry at ALL about quantity unless they're UNDER eating (happens with teething, etc.). Just quality. Make sure that formula is given first until they're done... and then let them play with table food. There IS a way to make sure a baby only eating table food gets enough nutrition, but it's extraordinarily complicated (lots of bone marrow, soup concentrates, almost no fruits/veggies -takes too much energy to digest- and those that are need to be mixed with saliva, ditto meats need to be pureed with saliva... like I said, it's complex. Myself and some collegues have had to do that for some babies in wartorn areas where there are no supplies and no nursing mother until supplies can be brought in. Just imagine how much table food YOU would have to eat to double your weight and 6 months! Breastmilk and formula is SUPER concentrated and already broken down. Rather like eating 5 super sized meals from McDonalds for every meal every 3 hours while on an IV drip of vitamins and minerals).
So yeah... I wouldn't be too stressed about amounts (unless it's given before formula)... and just get her to write up a list of everything he's eaten every day.