How difficult is it to bring someone back from the dead?
The opportunity isn't miss-able (unless you have opportunities turned off), and will happen on it's own automatically after enough days pass by.
Once you have your playable ghost (by completing the opportunity) your deceased sim is able to do everything they could do in life. Yes, everything.
This means she is able to cook just as well as when she was alive; if you have the ingredients for ambrosia, all she needs to do is cook and eat the recipe and she'll be returned to her mortal coil.