Our Chairman/CEO is clearly an insider under Reg O as he is an executive officer, director, and principal shareholder. His wife owns approximately 2% of the bank. Does she therefore fit the definition of principal shareholder (215.2(m)(1)) because she (a) indirectly owns or controls or has the power to vote more than 10%, and (b) shares owned by her husband, the CEO, are considered to be held by her because they're immediate family?

Yes she would be for the reasons you recapped.