At that age a mixture of WiWo and PD (honestly) seems to help. Whenever he gets up, put him back down, say night night, go back out. First night will be like 200 times and UTTER exhaustion, second night less...
So as soon as he gets out of bed when she leaves the room she should carry him to his bed, say night night (and his name) and then leave. Then he'll try and get out again, thing repeats...
I've seen that work