Hi hassie1 ... on a package holiday, the permitted luggage allowance is specific to the tour operator rather than to the airline.
Easyjet have a free baggage allowance of 20kgs, however there is a charge for each piece of luggage checked into the hold. Passengers booking direct with Easyjet can pay that baggage fee online at a reduced rate, or at the airport at a higher rate.
The Cresta Holidays website is unclear about the free baggage allowance, however they are clear in saying that a baggage fee will be advised at the airport. My guess would be that Cresta will allow your daughter a free baggage allowance of 20kgs, but she will be charged a fee per checked bag by Easyjet. There is no fee for hand luggage. However, that is only a guess and for absolute confirmation, it would perhaps be a question for Cresta rather than Easyjet. Presumably the booking confirmation is no clearer than the website ? You say that you have posted in Complaints, but it may actually be worth posting in our Tour Operators forum in the hope of catching the attention of someone who has been on a similar Cresta holiday.
David