So, a good lip balm needs to have two types of moisturizers in it: humectant moisturizer and occlusive moisturizer. A humectant moisturizer actually does sink into the lips, and then pull moisture from deep within the skin. An occlusive moisturizer then creates a barrier on top of the lips to hold moisture in. So, obviously, you need a lip product with both. A lip product with only one of these isn't going to work and will actually make your lips more dry. Petroleum jelly was originally used as a medical salve, and it is a great occlusive. I'm assuming that most women who only use an occlusive, are doing pretty well with keeping their skin moisturized at all times, and that makes it really effective, as it locks in all that great moisture you have. But, if you really want to heal your lips, I would recommend replacing any lost moisture deep in the skin with a humectant, like hyaluronic acid or glycerin, which will concentrate moisture and pull it to the surface of your lips, and then sealing it in with an occlusive, like petroleum jelly, shea butter or beeswax.
There are definitely women out there that have medical issues, or severe chronic dry skin, that lack moisture deep within the skin. Sometimes, it's due to medication, or medical conditions, and sometimes it's just genetic. Just because using an occlusive only, works for someone you know, doesn't mean it will be all you need. Granted, it will work for a lot of women, but if you are still having issues with your lips, check the ingredients of your lip product to make sure they have both these types of moisturizers in it.