So my wife calls me and says that when she tries to put gas into the tank of her 2000 w210 wagon at the station, it will not go in and instead immediately begins to overflow out of the filler neck. She has ~1/8th of a tank left. Is there a valve in the filler neck that closes at a certain pressure to prevent over-filling? Is the line to the charcoal canister blocked or the canister bad? Can a related hose be disconnected to fill the tank for the time being? Is there any way to test this? Are all those things dealer parts? Thanks!

UPDATE: My dad just helped her and put a gallon of gas into the tank via a gas can. Does the fact that the tank can be filled by a can suggest any particular component failure?