Hi Empty, glad she's settling. in. We estimate that for a skinny, scruffy dog you should allow 4- 6 months to get the condition right, and by that I mean, good muscle tone, healthy weight and a really glossy, shiny coat. So the first thing to say is that you should be continually telling yourself this is a long term project, and don't beat yourself up that she's not looking fantastic straight away.
Here's my patented greyhound rehab plan- 
- some of which you are already doing.
Make sure worming/parasite control is fully effective and up to date (this will help ensure what she does eat can be absorbed to the fullest extent)
Develop a good programme of exercise for her (this you are already doing)
Grooming - she will be losing that awful rusty "kennel coat". Give her a daily groom outdoors with a hound mitt - she will probably love it. Gentle, rhythmic, sweeping strokes. After around 5 minutes of this, you can finish off with silk polishing cloth. This will help accelerate the loss of her old coat and the coming in of the new, shiny,glossy coat. You haven't mentioned if you bathed her when she came home. If her stitches are healed, then I'd give her a bath using a good quality dog shampoo (we use the canine version of Paul Mitchell - really nice).
Food - what are you currently giving her? I think you feed both dogs twice a day? That's fine, but I'd give her slightly smaller meals at that time, made up of more nutrient rich food, PLUS I'd allow her to have a third small meal. Sometimes if a dog has a poor appetite and needs weight on, this can be the way to go. We have a similar dog who was too skinny following an illness, so we are giving him extra poached chicken. We buy the cheap frozen chicken boneless breasts from Tesco and I poach them in the slow cooker. These are then added as a supplement to his main meals and he gets an additional breast as an extra small meal. You could vary this with other meats or fish (say a bowl of sardines). Sardines and eggs are excellent - one friend swore by a bowl of scrambled eggs for her hound each morning to get them back up to speed.
Finally, perception. Racing weight greyhounds are very skinny. But, remember that even a retired greyhound should always be light, and if your dog is otherwise healthy and in good nick, it is FAR better for them to be underweight slightly than over. Most people see greys and think they are very thin, because they are so used to seeing fat dogs. Obesity is a much worse condition for any dog, because of the pressure it places on joints and the risk of things like diabetes, heart problems etc. I'm guessing you had her weighed when she first arrived - depending on size aim for her non racing weight to be between 2 - 4 kg above that, and review again when she reaches it. Eventually, you'll be aware of the hip bones but they won't be so prominent, and ribs will be less visible though you should always be able to see the last two or three.
Good luck!