Your daughter's ability to get coverage abroad (which calls, texts & mobile data rely on) is dependent on roaming being activated - which allows her phone to connect to foreign networks. Data roaming is simply a phone setting enabling the use of mobile data whilst already roaming.
Has your daughter used her phone abroad previously, did she receive a welcome text message on first arrival abroad? These are good evidence of roaming being enabled if so. In these cases, manually cycling through all available local networks often resolves issues - toggling flight mode can have the same effect.
If not...On PAYG, roaming is auto-enabled once your phone is used in the UK first. On pay-monthly, this needs to be enabled manually - usually by texting ROAMING to 150 before leaving the UK. Did your daughter do this?
If your daughter is on pay-monthly and now finds herself abroad without having enabled roaming, her only recourse will be to contact CS to request it activated. The account holder can either contact +44 7953 966150 from another working phone, or +44 800 9566000 using a web-calling app over WiFi.
