Whilst the advice given so far is correct for most folk, it can be different when folk work different days each week. If someone works different days each week it can get a bit complicated when it comes to waiting days and Qualifying Days .
To make it easier to administer, the employer can have an agreement that no matter what the actual days had been worked or were to be worked, certain days are classed as non working days. It may be that this particular employer says that Saturday and Sunday are non-working days and that also means they were not Qualifying Days.
As waiting days must also be Qualifying Days, Monday-Wednesday would be classed as the waiting days and not Saturday- Monday. If an employer has this type of arrangement, it has to be agreed with the employees too so it's possible that this applies to the daughter but she has forgotten about it or was not made aware of the fact.