I agree with you that Faith is strong and smart but here there is a timeline issue. The Cruciamentum has to be done the exact day of the 18th birthday and as Alkeni noted Faith's 18 birthday happens later, probably when she is in coma, that's why she never went throught the test. But if she hadn't been in coma how would she have been? remember how she acted when she swiched body with Buffy? she was totally out of her mind, how could she be able to take out a vampire like Kralik without her powers? I don't think she could, not at that time of her life