Sorry about your hen's broken leg! That is so sad. I have seen many people post about how chickens rarely make it through surgery due to the anesthesia. I think it is just too taxing on them.
As far as your buff orp, this thread may help you out - http://www.backyardchickens.com/t/506157/think-that-my-girl-has-ascites-update-chicken-better/10. gallusdomesticus said: "You'll need to treat the underlying cause of ascites. There are several causes but the two most prominent causes are congestive heart failure and fattly liver syndrome. There's not much you can do for the first cause but you can treat the second. Don't give her sugary treats such as fruit or bread. My vet prescribes milk thistle extract which I give her every day. People and animals use it to aid liver health and you can buy it over the counter in health food stores. It's normally in pill form which can be crushed and mixed with water to be squirted in her mouth with a syringe. It won't cure the ascites but mitigates the symptoms and delays the need to have her abdomen drained."
I'm trying to hang in there with Buttercup, it's just so heartbreaking to see her go downhill. Tonight my husband said he saw some older pictures of her and said he was shocked at how much she has changed in the past few months.
Good luck with your girl!