I would NOT feed her only canned.. There is not enough protein in a can of cat food (it's only about 10% max) to sustain a cat. A high quality dry food such as Innova, Wellness, Felidae, etc is all she needs, plus plenty of fresh water. On a high quality diet, adult cats rarely need more than 1/2 to 3/4 C of food per day. Some adult males prone to obesity do fine on 1/3 C per day.

I definitely agree with feeding her meals. They have something to look forward to and it gives them a routine.

If you can get her an appointment to have a fecal done and possibly have a dental done on her, it would help shed some light on her fussiness. Cats are very prone to dental disease, so having dentals done regularly is key. Some parasites can also make them anorexic, not wanting to eat.