Sounds like my little man. He weighed 14 lb 4 oz at 3 weeks! And he spits up after almost every feeding, but not always right after the feeding. I've noticed that the longer he waits to spit up, the worse the milk smells. It just smells like digested milk. Let milk sour in your fridge and then smell it. The bacteria are digesting it, and that's why it smells. Smell kefir or yogurt--which are also digested milk--and you'll see what I mean.
So notice, or maybe make a chart, if you're so inclined, about what it looks like and how long it's been since she ate. You'll probably notice that it's chunkier after an hour or two, and runnier if she burps up right after eating. This makes sense. Milk curdles in acid, and the stomach has acid. If it smells sour, it's probably been an hour or two as well, since it's digesting.
My pediatrician said he burps up milk because he's getting too much. This makes sense, because he's so big, and my daughter, who was always at the bottom of the percentile, almost never burped up milk.
So personally, as long as she's gaining on her curve and isn't underweight, I wouldn't worry about it. I almost never had to burp my daughter, but now I leave burp cloths lying around the house so I don't have to go far to get one on short notice! I'll be glad when he gets past this stage!