Just to add to all the good answers already given:
If she's going to be working abroad for a long time (the entire period of summer) then it's probably going to be better for her to also buy a cheap phone abroad (PAYG on the foreign network) as well as having data and roaming on your 02 contract phone. At least then she has the option to turn data/roaming on or off from her phone whilst abroad but still have it there as backup. The PAYG phone can be used to keep in contact with her friends in the country she is working in. My friend from Germany does this every time he comes over to the UK (PAYG UK Network provider).