That's a tough one. To me it would depend on whether I felt that she was responsible enough not to abuse it.
If you feel that she is responsible then a credit card can be an excellent way for young people to establish credit.
If she is a fulltime college student there are some really good card offers available such as:
If she is not a full time college student then she will have consider offers such as:
Again I think the key word is responsible. I've seen credit cards build young peoples credit and I have also seen them ruin young peoples credit.