I'd take it seriously and agree with your dh on saying look you don't have to go on the trip, you do have choices in life.
I've got loads of suggestions to ignore/try, based on last year with my son in yr 7.....
extra sleep for you in the day to help with all the emotions going round
breakfast in bed for your dd
supper/tea in bed for dd
sit with her and chat at bedtime , maybe until she's safely asleep, night after night
ask all about teh other friends, list of what they are good at, bad at, how rude can they be, funny things they say, who's fastest at changing for games
take dd and friends swimming or anything at the weekend
bouncy castle in the garden for them to enjoy one Saturday
be really gentle about days off, I kept my son off if I could see from his face that he was having a wobble, otherwise he'd go into a spiral of worry/tiredness/aloneness. He'd be so much more cheerful after a days break
Yes, I'd talk to the year head, head of school, any teacher she says is friendly as a starter.
hv could be supportive, may well have children that age too
say over and over, we are on your side, you are so brave to have told us how you feel, we will sort this out, we love you so much, there is a way forward even if we don't know yet what to do.
really be honest and open, swear if necessary, admit you don't know what is for the best, keep the talking and showing of emotion going.
dvds after school, chocolate, hot water bottle and duvet on the sofa,
It is a total nightmare when they are unhappy. Anything to get you through...