Hello bro, and hello to the wife. Sounds like she has made some good progress and is motivated in the gym Good for her, and lucky you! At 40, she is far from old, and with more time, her skin will tighten up. It can take awhile, and it depends on how far it was stretched out to begin with.
As for what to take, first off, she needs to eat to grow, just like you or I. That is going to be the key. Losing fat is just a matter of eating fewer cals, and can be eaiser than gaining muscle for some. Gaining muscle can be especailly hard for females. Still, it can be done. If she wants to look into steroid use, she'll want to be very careful. These are male based hormones and although they are a key to growing rapid muscle, they also can come with masculinizing side effects. So be sure that she reads up about that here, by searching the QA and info about females and steroids.
So if she wants to move forward and work on adding mass, Anavar at 5mg to start would be a good direction. Then move to 10mg, after a few wks, if she is ok with it. It's the most mild of all steroids and works well for girls. I would suggest that she ran it for no longer than 8 wks at a time, then took 8 wks off.
GH would be another direction to go, but it is a long term commitment. It would help long term with muscle gain, at a very slow rate, as well as improve fat loss and tighten her skin. Between 1-2iu would be beneficial