LOL! The past 5 years my DD has just done summer trips overseas in Scotland, Italy/Germany and Spain. To communicate she would use Skype and What's App ("it's used everywhere") for calling and texting; for money I would send a couple of credit cards and some pounds/Euro (if she were for longer period I would have sent a debit card though), and not worrying...well, if she wasn't texting I knew she was having a good time so I used no news is good news philosophy. I believe one of the Cali ladies (either calfan or californiagirl09 [they travel together so I get them interchanged] has a DD in England studying) so hopefully she'll chime in.
ETA- Funny story, one summer when she was in Scotland, someone broke into her dorm room and stole her money. She would offer to run errands to the Tesco right before lights out for anyone wanting late night snacks and she'd keep the change. This is how she got by with very little cash. I asked her why she didn't use her credit card and "you said that was for emergencies, Mom." Not sure what an emergency is if it isn't being away from home with your money stolen, but I was proud of her initiative!
Also, it helps to know who is in charge of the program where they are studying and good contact numbers just in case-for your peace of mind. Then take a deep breath and know that you've done what you could do in raising an independent person. Good luck