This system is promoted by Tony Robbins, who has always seemed to me to be an obvious charlatan and I share your skepticism of it having any effect at all.
Some dentists do offer this, so the charitable interpretation is that Meghan was given this by the dentist and had no idea she would be photographed.
My less charitable interpretation is that this is more likely than not a paid promotion opportunity staged to look like a paparazzi shot, which is a common Hollywood tactic.
A bit off topic but I saw Tony Robbins in NYC through the Oprah Winfrey show. He is definitely charismatic and can get the audience so excited that they can do and be all. My feeling is if this works for her so be it. I have never heard of this before but I know people are searching for things to reduce stress and anxiety.