Okay, I've read the days responses and some were positive advise, but I'll tell you the read deal here.
1st off i am a 23 y/o female who's given birth twice, and my BF has a very large and thick cock and I'm as tight as the day the 1st man ever entered me.
Get rid of the original OB/GYN crack pot! Find yourself a reconstructive surgeon who specializes in Vaginal reconstruction. I do not believe your wife is doing her Kegel exercises, she is way too big for you to be slipping in and out. The minute amount of pain and discomfort she is going to experience is going to save her marriage and the father of her children, so its worth every discomfort she experiences. Quite honestly its her own fault because she became lazy and has never done anything about the exercises she was told to do since birth #1....
Listen to me, take my advise and hurry to get this procedure done, its worth every penny you'll spend!
Good luck, you always have Mary and her 4 sisters to help keep the wold away till she gets tightened up!