What is the difference between 太太 and 夫人?
In modern Chinese: 

太太 is a common title for "Mrs." or a noun for "married woman" (in general)


  Mrs. : a title used before a surname or full name to address or refer to a married woman, or a woman who has been married, without a higher or honorific or professional title.


夫人 is a more formal honorific or title for "Madam" or a noun for "married woman" (of high status)"


  Madam :(often initial capital letter) a polite term of address to a woman, originally used only to a woman of rank or authority:


In short, 太太 is a general title for married women; 夫人 is a more formal/honorable title for married women; 

女仕 is another honorific for women. A formal/ polite term for addressing to adult woman  (single or married) 

The difference between 太太 and 夫人 is somewhat similar to San (さん) and Sama (様) in Japanese