The last thing you want someone to do is to show up and knock loudly or ring the doorbell when you just got the baby to sleep. Place a cute sign on your front door, and guests will figure it out pretty quickly. This is one of those unique baby shower gifts that will be a gift that keeps giving.
Yes, she many get white noise machines from other friends who know how amazing these things are… but I doubt she will get a travel sized one. Specifically, a Rohm travel sound machine… it’s more expensive than a regular one, about 5x louder, and about 10x more useful.