See, that kind of irritates- the idea that only people with children understand the true meaning of tiredness!
My first dd was a terrible sleeper, and yes, I spent many horrible tired nights trying to settle her.
BUT long before I had dd1 I was a large animal vet. And I can tell you now that getting up, stumbling to the next room and sticking a baby on your boob is far easier (and, dare I say, less tiring?) than answering the phone at 2am, getting up, getting dressed, driving miles in freezing fog, stripping off, spending an hour and a half trying with all your might to calve a cow, finally managing, washing yourself off in freezing water, driving home, falling into bed (with aching arms and afterbirth hanging from your ear), only to be called out again 20 mins later, then by the time you get home it's time to shower and get to work.
Now, obviously I'm not suggesting your colleague is moonlighting calving cows (or maybe she is- who knows!), but being tired/ having sleepless nights is NOT just a parent's prerogative!!