(Another) City of contrasts

So what is the word that describes the relationship of the sister of my (future) son-in-law?  There must be something to explain this special connection...??
We met and had a wonderful walk along the South Bank of the Thames, enjoying her favorite sights and places near her new home in London.  Many, many to choose from, but this contrast of the Tower Bridge and the new City buildings (we laughed that "Walkie-Talkie" in Engish, is "Talkie Walkie" in French!) was particularly indicative of the excitement and diversity of London...