Are you traveling with a lot of luggage? If not, maybe think to use the Elizabeth line and transfer on to the DLR - I would look at the day time flight from ORD to LHR the day before - it will reduce the risk of a miss-connect. You only need a two hour delay to cause issues. I suspect you would get rebooked as it is all one booking, if there was a delay to your inbound - this could work in your favor as they may book you on a LHR-AMS flight.