It's a balancing act of giving them freedom and independence with what you feel happy with. Kids do need to experience these kind of trips - but each child is an individual and unique and each family set up of different, so what age works for one child/parent isn't the same for others.
Op - I am also a single mum, so get the not having someone to bishbashbosh it with. (Although I do use my mum for that - but it's not entirely the same as she has a grandparents perspective and it's not the same as a parent one).
When I went to primary, we had local overnight activity trips in year 4 and 5 and also French trips in both years 5 and 6. My son went to the same primary, and the French trip was near identical to that I went on, same place, same activities, same accommodation. Because I knew it all so familiar with the set up - I was happy for him to go (he was year 6 as they now did it every other year). It was familiar to me, and it was exactly what I had experienced as a child so it felt right that my child did exactly the same. And it went fine - he loved it and I survived!
However, if they had been sending him to Spain I definitely would have had second thoughts and struggled to find it too. I'm not sure I would have sent him to be honest. It would be difficult to know what to do. On one hand she really wants to go- but on the other it's the cost of it, the distance away and also having to commit so far in advance.
My boy is nearly 15 and I gotta say it's still hard sometimes letting him go off on camps - yes we have had a couple of disasters in the first years of secondary where things didn't go too well (he got sick on two successive trips away) but he survived them.
I got cold feet about a large trip which was very unknown to me earlier this year - luckily the flights had already been booked by someone else so I couldn't back out and say he wasn't going. And I am so glad I didn't - it was the making of him. Yes I know my boy is 5 years ahead of you dd, but I have had to train myself to let him do these things and not be overprotective. If you don't let them then they can't learn to do things independently. It's a really hard line to walk.
But with parenting - we make mistakes and hindsight is a wonderful thing. for now, you just need to sleep on it, chat about it with your daughter and to the school, look at finances, speak to parents you know whose kids have been on the trip, to your dd's friends parents too. Then decide.