No more than two infants per accompanying person are allowed. Infants under two weeks of age will not be accepted for travel.
Children aged two years or over must occupy their own seat and pay the same fares as adults.
It is the accompanying person's responsibility to ensure that the minor is adequately secured into the aircraft seat. To this end easyJet will accept a car seat supplied by the accompanying person for any child over six months for whom an airline seat has been purchased, provided that the car seat has a rigid metal or plastic frame, is no wider than 42cm, includes lap, shoulder and crotch straps, and is upright and forward facing. The required restraint device for the age of the infant is detailed below:
The above text is from the Easyjet websites terms and conditions.
Looks as though the seat was wider than 42cm and thats why she was obviously refused travel. Cant really blame anyone I dont think, Obviously the passenger didnt get the tape measure out!