Sorry. for the confusion. I wrote the post while trying to juggle several things at work at the same time.
So, yes, I talked to my daughter about it. She is actually the one being anxious what would happen when she has her period, epecially on the watersport camp. I remember reading about medication to skip a period but as I said, I was on the pill when I had issues where it was helpful to avoid a mess and therefore don't have first hand knowledge.
She was on her period before when she was camping with the Scouts and hated it as the facilities at the campsite were less than ideal (think chemical toilets) and no real way to dispose waste discreetely. The camp is only 4 full days plus 1/2 day travel, so she would miss basically everything. I don't have details yet where and how they will stay but knowing the group tents in a campground with shower/toilet blocks are definitely an option.
Speaking to the GP - yes, she can do it on her own and I would say she is confident enough to do so. But, she is also ok with talking about this with me and the last two GP appointments were very much her talking, I offered to not go in her with/not be on the phone but DD declined, she was happy for me to stay. I do agree, no GP should prescripe medication without her knowledge and taking it into account.
She has used tampons before when she went swimming, she did lifesaver courses until lockdown so she knows how to handle them. Normally that would be my first approach but a) she still has her period pain and feeling nausea and b) the issue with changing/toilet facilities.
I think a mooncup wouldn't work, as cleaning it would be even more messy.
We are a family where periods and sanitary products are openly discussed, I bleed very heavily (I turn 50 this year, no signs of stopping) and DD always knew about it and talks even with DH in the room about it. He knows how to deal with two females in need of painkillers, chocolate and hot water bottles.
Based on some of your comments, I think it may not worth it if it just screws up the next period.
My post was very much a research question. I am not controlling but I have a very anxious DD (she is actually under assessment of panic disorder) and this is a form of fact gathering mission as I think she should know what could be done and what side effects are.