Hi, I've just returned from 2 months in Tanzania from Arusha, moshi and stonetown and Jambiani, Zanzibar. I volunteered for one month and then backpacked for awhile. As long as your daughter is not extremely naive or goes out when its dark alone, flaunts her cash or is generally flirts with danger. She should have a wonderful, safe and glorious experience. I had no problems and tanzanian people are warm and friendly if you take the chance to meet them. I understand if you have reservations, if you have any questions or want to contact me go ahead. Also, check out www.bootsanall.com. They have a great travel forum. Good luck to her and she will be just fine. Oh, she may want to learn a little of swahili. I feel it helped quite a lot.
good luck!