Difference between 小老婆 and 小老太
Should I call her 小老婆 or 小老太? Is it rude to call her 小？


Don't use either of the two expressions to address ladies. 小老婆 means concubine. As for 老太, ladies' reactions towards that expression vary. Some ladies may feel insulted and others complimented. 小老太 is rather strange to me, although it might be used by areas I'm not native to.


How come flowery-auntie-mother suddenly became a young girl??? Strange!!


Do not use 花姑娘 either. It is almost only portrayed as an expression used by Japanese invaders to refer to girls they wanted to insult.


what is the difference between 小姐子 and 大妹子？ Who is older?


I don't think the expression 小姐子 exists. 大妹子 is quite similar to "sister" used by black females to talk to or about each other.


So old-old lady suddenly become your wife??


It does not happen suddenly. 老婆 used to have meanings of both old ladies and one's wife but now the latter prevails. 


Does 老太婆 mean wife or old lady?


Both. But it is offensive to call an old lady 老太婆 if you two are not close.

So, just call her 婆婆 or 奶奶. I have not seen an old friendly Chinese lady who does not like these two titles.