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Are these cards she actually uses/needs/has access too? If so, then for that purpose it is neither good nor bad, since you state she is responsible and does not abuse that priviledge.
As for CR, that many AU's is not really doing more than a couple would. Your oldest couple tradelines is probably all that really is necessary to do the trick:
1. Establish Oldest Account/Age
2. Utilization
3. Opens her credit file (even though if you had waited till 18 then added her, it would do the same thing).
However, since she cannot apply for credit in her own name, whether you add her now, or add her to those same tradelines in 2 years makes not difference. The benefits of AU will go unrealized until she is 18....so it's kind of like a tree falling in the woods....nobody there to hear it, so does it make a sound? In the case of her CR....no.