Practice when her next period starts so that she'll be ready by summer. My first experience of trying to insert a tampon was in a dingy, dirty public bathroom at the lake with my mother standing outside the stall giving me directions when I was twelve. My mom used Tampax, and I found the cardboard applicator dug into the walls and was uncomfortable on insertion. Not surprisingly, my attempts didn't work and I ended up wearing my shorts over my swimsuit that day.
I didn't try again until the summer after eighth grade when a free sample came in the mail. Then I did some experimentation on my own and in my own time. The thing that caused the most difficulty was that I had no idea of how to insert it and where. (Ha, Ha, I know :) ). So I took the hand mirror, put it on the floor, crouched over it and looked, saw what needed to happen, and then I could be successful in inserting them. I'd recommend that to anyone.
Of course the free sample in the mail were the kind that were linked to toxic shock syndrome deaths soon afterwards. I had been wearing mine too many hours in a row (they were so absorbent that there was no need to replace them often) and I didn't want to "waste" them, so I wore them for long spans of time, even overnight. Luckily, I was an avid newspaper reader, found out about the issue, and I changed my habits. My mom never inquired about it when the news hit. Now that I look back at it, wow!
Please read up on toxic shock syndrome and get recommendations from your Ob-GYN for types and the regiment for wearing them for teens. I personally know of deaths of young girls linked to the wearing of tampons for too long of a duration. For my daughter, my requirements will be that she must wear a pad at night, and that she can wear them only for four hours each.
I'd also talk with your daughter about her willingness to speak with the counselors at camp. She's been there before. Does she think she can talk with them about getting help? If so, send her. Who wants to look back at a childhood and remember, "That's the year I got my period and I didn't go to camp"?