matron of honour 
noun
A married woman attending the bride at a wedding.We have the clothes, food, a best man, a matron of honor and now flowers....
- The order of entrance is as follows: parents of the bride, parents of the groom, ushers with bridesmaids, flower girl and ring bearer, special guests, best man, maid / matron of honor, bride and groom.
- I'd chosen two of my nieces as bridesmaids and my best friend in the whole world as my matron of honour.