Switched to canned. Should I measure and limit food

My cat has allergies. I've finally found natures instinct ingredient turkey works. As far as feeding her only wet, should I measure and limit it? I just pulled dry a couple days ago. My friend said let her have as much as she wants but she really likes it. She's at 12 lb Maine coon female and I give the 5.5 ounce cans. It looks like she should eat 1.5 cans daily. She acts like she'd really eat 2 or 2.5 cans daily if I let her. Anyone with advice and suggestions.

In general cats need around 20/cal per pound of weight. So look on the can and see how many calories are in a can of food to figure out how many cans she should eat per day. 

Just feed your cat enough caloires daily. Your 12 lb cat may need around 250 to 300 calories daily to maintain weight. A 5.5 oz can of the NV LID turkey is 212 calories. So you need to feed about one entire 5.5 oz can plus either not quite half of another 5.5 oz can or half a 3 oz can daily. Adjust amount of food according to your cat. She may need more or less food. Split the food up into a few meals daily to keep your cat's tummy happy.