Your friend's photos aren't stored on the SIM anyway. They're either stored in the phone's internal memory or on the mini/micro-SD card that she's slotted into it (which has nothing to do with the SIM).
Further, if she switches to a different deal from the same provider she won't need a new SIM.
£17 for 500 Mb is ludicrously expensive but (given that 500 Mb is nearly enough for her needs), changing to a deal that offers 120 times as much data is ruddy silly too. If she switches to Asda mobile, for example, she can get 5 times as much data as she currently gets (2.5 Gb), which should easily be enough for her needs, and pay just £7 a month for it. (Switching to Asda Mobile, or to any other service provider, would involve changing the SIM but she could keep the same phone number and her photos would be unaffected).