Why does she think she knows everything?

For a few weeks now my 5 month old granddaughter has had a little rash on her bottom. We've been putting Desitin on it but not much improvement. She uses Huggies brand diapers. Last night my daughter called me to say that she's in a mommy group and one of the other mommies said that her child use to use Huggies and also had a rash on her bottom and she discovered that there's some sort of chemical in those diapers in reacts to babies skin that causes irritation and rashes. I told her to stop using those diapers and to switch her to Pampers brand. When I told my wife about it I mentioned to my daughter that I had some antibiotic cream she could use to help heal her bottom. My wife said not to use the cream but to just put some Vaseline on it. I told her that Vaseline has little to no healing properties and all it would do was put a barrier between her skin and the diaper. Of course my wife thinks she knows everything and said not to put the ointment on her and to just use the Vaseline. She wants me to think that I'm just trying to over rule her but in this instance I think I should. Who's right here? Are there healing properties in Vaseline or is it just a protective barrier and what's wrong with putting some antibiotic ointment on a baby's bottom to help clear up a rash? She feels that when you don't take her advice you're saying that she's completely wrong and no one should ever listen to her. Yeah, she tends to go way overboard on certain things. I've done some research and found that Huggies brand diapers have been notoriously known to cause rashes and irritations on baby's bottoms. There has even been a class action lawsuit filed.