Something else I find slightly odd, is the decision to change her baby on the car seat rather than walking into the store and using a bathroom which would likely have a changing table. I absolutely get changing your baby in the car if you're not near a restroom, can't leave where you're at, baby had a blowout and you don't want to carry that into the store, etc. but she was already on her way into the store to buy the mouthguard.
I don't know. I just never found it easy to change my kids on the seat of the car- although I have done it on rare occasions. I also live in a different part of the country where most public stores have bathrooms for their patrons, so that may be influencing my view on this.