It sounds like you are trying to feed her healthy foods, which is great, but at 13 months, she really shouldn't need fat free anything (unless she's on some sort of special needs diet?). Natural, unprocessed foods are best. If you're worried about fat content, keep in mind that studies show that natural fats are much easier for the body to break down than what's in the processed stuff.
13 months old is a time when a lot of things start happening at once.... she's starting to be more active, she's learning more, she's talking more, she's starting to understand more.... everything is accelerated and her body is using a lot more energy and so she will burn through calories a lot faster.
It might not be that you aren't feeding her enough
, it might be that the foods you feed her don't stick with her for very long. Snacks and meals should both consist of healthy foods that are filling.... that doesn't mean bigger portion size to make her full, it means you should work on putting the right foods together that will last longer in her tummy.
For example, you could add some sort of cereal to her breakfast. Rice cereal, instant oatmeal, dry cheerios (or serve them with milk), cream of wheat, etc.... Rice cakes could be eaten with yogurt or cheese, applesauce can be mixed with cottage cheese or yogurt.... things like that.
My 15 month old still has three (occasionally four) 8 ounce bottles of milk a day. I was always under the impression that until they are two years old, a child should be getting about 24 ounces of milk a day.
Hope this helps!