The girl I mentioned has not had all contact cut.
She just doesn't have her own phone and she does not have the expectation of privacy in phone and internet communication that many of her peers have. She has her own email address (just one) but her parents know her password. She is allowed on FB under strict rules of engagement, with her parents allowed to oversee her account, and no membership of secret groups allowed. They have a compact. (DD4 is not on FB however, by her own choice, so that is ruled out as a means of contact.)
She spends time with us regularly (they moved a few hours away so this happens when they are in town visiting relatives every few weeks) and she and DD usually have a sleepover, chat, goof around, go to the movies, go out for a coffee, look at the shops, sit in the park, listen to music, play with the cat, draw (both like drawing/art) - all the usual stuff people do when they are friends and share interests. She is also out at school all day every day and at school clubs that she enjoys. She does not do a sport any more, as excessive exercise was part of her anorexia profile. She does daily PE at school.
She can use her mum's or dad's phone if she asks, and DD can send texts and emails via her mum's phone, and email her. She can use the home landline. If there is something she needs to say to someone during the night she can wake her parents or use the landline to call either her doctor's 24 hour emergency line or the Samaritans. Using the landline requires speaking and it also potentially involves waking friends' parents at odd hours if she tries calling umpteen friends to try to make contact in the small hours of the morning. Before the rules were put in place she would text multiple friends at night if she felt the need, and would possibly get a response from someone, almost like fishing. The friends did not know that they were the fifteenth (or whatever) person texted. Each thought she was specially chosen. It wasn't helping her on the road to wellness and it was stressful for the friends.
So DD and her friend are in contact, just not after 11pm/midnight, and the friend's mum is aware of how much contact there is with specific friends.
This has been a long, hard road for the family. They nearly lost their beloved daughter to a horrible illness that was exacerbated by contacts online, and she is still not out of the woods. They are hoping she will be well enough to go to university away from home, which will be decided on in just under 2 years.