Sleep training at 4 months - are we insane?

My wife wants to start Ferber method with our 4-month-old because she's back at work and absolutely losing it with the night wakings. I'm on board with ANYTHING that gets us more sleep, but our pediatrician said 4 months might be early. Has anyone here actually done sleep training this early? What was your experience? We're in Portland and have a Huckleberry subscription if that matters.