Irene is so drunk that she has problems with the way she walks. It is either she bumps herself on the wall or she would repeatedly fall on to her knees which is why River has to wrap her arms around him for support while they make their way inside his car.
When he successfully placed Irene in the backseat so she could comfortably lay down, he went to the driver's seat. Before starting the engine, he checked Irene's position and he was relieved to see her sleeping soundly.
He takes his phone from his front pocket and dialed Valerie's number to ask for their address so that he can drive Irene home so she could get some rest. During the entire night, she was the one who drank the most alcohol.
The phone rang twice before Valerie picked up the call, "Hello?" She sounded suspicious because the call was coming from an unknown number.
"Valerie, it is me, RIver." River introduced himself in order to not freak her out of some sort.