Honestly... Tell her to get her shit together. She needs to know that you're displeased with what she does with her free time, and has an apparent lack of concern for her self-image. Don't just let it slide, because the longer you do... The worse the issue is going to get. It's not OK to become complacent in a relationship and let your body go to shit if one of you is still working hard to maintain yours!
These situations usually go a little deeper than the other person simply needing to get their act together.
I guess first, you have to ask "is this who she was all along before you ever married her and put a baby in her"? Some girls are just not into keeping up their physical appearance and NEVER will be. Not that that's an excuse to let ones self completely go, but if that's who you marry, that's who you'll be married to.
Second, and sorry for asking @rickygear2 but I am unfamiliar with your background, but is lifting/using AAS something you were into BEFORE you got married to her, or did you get into this lifestyle after you and her got together? This may not apply to you, but sometimes a couple is already together AND THEN one of the individuals gets into fitness and exercise and diet and improving physical appearance, and at that point, it causes feelings like what you have expressed. In that scenario (and again, this may not apply to your situation at all) the expectation that the other person all of a sudden get into exercise/weight loss/physical appearance is the equivalent of that old friend or family member that discovers religion somewhere along the line, becomes a Jesus freak, and then starts casting disappointment and disapproval in the direction of the "sinners" around them for not having the same new interest in God that they do.
I am not trying to point blame as obviously we don't know the pre-existing dynamics of your relationship with your wife, just throwing some other thoughts/possibilities out there.