Look Satyricon, we're trying to help you. When YOU go on cycle, if you have half a brain, you're lifting like a maniac, you've got enhanced ability to grow muscle. To GROW muscle, you have to feed it, consequently, you're hungry.
Now you're telling us you got a woman who has NO appetite, is a former dancer (who are notorious for having major eating disorders) does just bodyweight exercises (which generally do not enhance muscle growth) and is so underweight she's got ZERO energy. You want to give her an appetite with no sides. You know what she needs? Tell her to smoke some marijuana a couple of times a day so she has the appetite to get to a healthy body weight (which, for a 5'8" woman is between 122 and 164). Get her to a normal, healthy weight (90, 110 I don't give a crap, she's underweight, which is why she's so exhausted) then she'll have the energy to start working out properly. Then you think about putting her on a steroid after you dial in her diet. You put her on var now you risk screwing her hormones up, if they aren't already messed up. If she's not going to be lifting, if she's not going to be paying attention to her protein, fat and carb macros, you're spinning your wheels. With women this stuff is REALLY critical, especially when you start messing around with women who are over 30.
Look, I have DJD throughout my spine and joints and probably the beginnings of arthritis, as well. I can work out with free weights no problem. In fact, bodyweight exercises are harder for me, because I have extremely limited flexibility. Weight training means being conscious of proper body mechanics, being careful with your form and knowing what exercises you can and cannot do.
If your wife isn't willing to get serious and log what she eats, then she's inherently happy being skinny or doesn't really want to make changes. The simple truth is, there are no magic bullets, not when it comes to gaining muscle, or to losing fat.