My wife has officially let herself go...?

the other day i was eating in a restaurant with my wife and the waitress thought she was my mother. how embarring. when i married my wife she was a solid 8...something to be proud of. now she has cut her hair into almost a buzz cut, gained weight, and wears sweat pants with holes in them. she is starting to look like rosie o'donnell. my friends' wives have taken good care of themselves and are still very attractive. i look for reasons not to go out with them now because i don't want to stick out like a swollen thumb. i am going to give my wife an ultimatum of either getting back in shape and growing her hair back out, or divorce. what is a reasonable amount of time to give her to get back to looking respectable as opposed to being the slob she currently is?