She's probably old enough to regulate herself in how much she will eat. Since she's so young she is growing like a weed and needs all that energy. Free feeding is usually best unless you have a chin that is overeating and giving herself digestive issues.
And, yes, poop is a great thing for a chin! Beautiful, consistent, firm droppings in great abundance is wonderful. It's when you don't get the droppings that you have to worry, like Tunes said...you'd have a sick chin in that case.