As I recall, Tika's plate armor was actually piecemeal, scavenged from fallen enemies, so that might justify the AC. And there's nothing wrong with her not being able to use her thieving abilities (she could take off the armor if she had to use them, but they're kind of shabby in the first place). I can't say anything as to her illegal dual-class though; Dragonlance was always a weird setting, since it was based on novels where the rules of D&D were never allowed to get in the way of the story. As a result, some rules are set in granite, and others are more like suggestions of rules, and you never could tell which way something was going to go.