Let's look at possible scenarios, Ilike.
If she does go:
Something could happen.
Yes, true, but something could equally happen when she is at home. You could both be run into, your house could catch fire etc. Frankly, if you are thinking of such accidents as a car crash, then your presence would not be any protection to her. One benefit with being on a school trip is that there will be at least one person who is trained in first aid.
What you need to consider is whether there are particular dangers about this trip that outweigh the benefits.
What if she cries in the night?
Someone will comfort her. Really, they will. And if you are really upset and finding her behaviour difficult atm, you might actually both benefit from a break.
On the plus side, she will almost certainly enjoy a new experience. She will feel she is able to do the same as her friends. Most children really do love these trips and the shared experience.
If she does not go:
Is there a risk that she will feel disappointed because you have first told her that she may and are now changing your mind (and it is very late in the day if the trip is tomorrow)?
Is there a risk that she will feel she is being punished and therefore that she is not as good as her friends who are allowed to go? And what will that do to her confidence?
Will she worry that you think she is less tough and capable than her friends if she is the only one who is thought not able to do without her own bed and comforts?
(this was an important factor for me in sending dd who had anxiety problems; I did not want her to think I doubted her; it was bad enough is she doubted herself)
It is impossible to say what good a 5-day trip will do for your 8yo dd, I can only say what it did for mine:
endless fun and giggles with her friends
a mind-expanding experience (educationally, this trip was very good)
the confidence that she could feel sad and homesick and still handle those feelings
feeling that she was as strong and capable as her friends and that we trusted her to cope
(extra important as she did have health and anxiety problems)
But obviously, this is just one family.
I just feel that if you did not believe that being away from home is beneficial for an 8yo, then you should have said so from the start. Now you have let her believe she is going and are changing your mind because you feel vulnerable. It doesn't seem like it is about her any more. Have you asked her how she feels?
Also, you have let her believe that if she does not go, it is as a punishment; if you do make her stay behind, it's going to be incredibly hard to erase that idea from her mind.