She asked if she could pack it in her 'carry on'. She didn't say anything about putting it in her checked bag.
OP: Yes you can carry it on. I too must have white noise to sleep and never go anywhere without my white noise machine. I usually put it in my carry on, but have also put it in my checked bag and have never had a problem. I fly with mine maybe 5-6 times a year.
Off topic, but: I picked mine up at Wal Mart for alot cheaper though. I have two and think I paid less than $15.00 for each of them, so if someone did steal one out of my checked bag, it wouldn't be that big of a deal to replace it. They are both Conair and have like ten sounds to choose from (white noise, rainforest, thunder storm, summer night, ocean waves, heartbeat, songbirds, train, running stream, and rain falling). I've seen the same ones at Target for less than $20.00 too.