So she had a lump, then it changed and a scab formed, then it opened up and all this nasty pus came out? Now you just have a cavity? You want to flush it with saline solution (google "Isotonic saline solution" and only use the one with salt and water). Make it up with warm (not hot) water, then using a syringe or something similar, put the tip of the nozzle inside the cavity if possible and flush it out a few times. Do not use ointments as this encourages it to heal on the surface but bacteria coudl easily be trapped underneath and the abscess will recur. Flush rwice a day until you can see it healing towards the surface of the skin. If a scab forms, soften it with warm water, and then gently remove it so you can continue flushing.