Sorry to come in a bit late. Wise words from anthropology. As a parent it feels awful that you can't Do Something & fix immediately. Sounds not surprising DD is having panic attacks. And not at all unusual to not want to see professionals.
Your friend & DD are not alone, believe me. She can connect up with other parents in similar situation through MN, School refuser or other forums - useful because you can see different paths that people followed.
Similar-ish stuff with DS 14. What worked was ramping down the expectations, letting him create a safe space at home: watching comedies & reading fanfic. Sadly we followed CAMHS advice for too long to "be firmer with your boundaries" and "just make him go back to school". Disastrous. "Pull your socks up" is not a treatment plan.
Usual advice: carry on being imaginative at finding resources & ideas for future strategies. DD might go for creativity, mindfulness, yoga, head massage, connecting with other teenagers in the same situation, CBT, horse riding, who knows. Right now let her do whatever feels good so she can feel safe. DS's psychologist suggests relaxation; pets; other social activities like baking, helping others; and special interest activities that give a sense of enjoyment, security and help social interaction e.g. online games, board games etc
GP is good (if not empathetic then change). If DD refuses to go then friend can go for herself saying situation is affecting her. GP can also be effective in future in driving other professionals. CAMHS - people have mixed experiences: good/bad, fast/slow so get the ball rolling. Check out other local resources for teenagers e.g. support groups. My DS now takes meds (fluoxetine) which he says helps with anxiety.
School - don't worry about it not that I would have said that 2 years ago. There is a lot more imagination now in how teenagers can access education - in school or at home, part time or full time. For instance my son has gone to school but done his work in a quiet room and he's had a tutor (from the LA) who comes to his home. When he feels a bit more robust that 1:1 tutoring can happen outside home e.g. in school or library.
And even though this drives me completely wild whenever a professional tips their head on one side and says to me in a soothing voice "make sure you look after yourself" it has some truth. For me this is
, sleep, watching comedies with DS & meeting friends for chats.