Yes, it is completely proper English and is the sort of thing that you would say but probably write in a slightly different way. If the author used punctuation

Yes, it is completely proper English and is the sort of thing that you would say but probably write in a slightly different way. If the author used punctuation properly then the sentence would be been something like this: "“I think, universally, founders and early startup leaders underestimate how hard people-work is,” she says." The person talking may have been using 'people-work' as a jargon term for team management, but otherwise there is nothing out of the ordinary about the statement.