Try to have regular playtime with your Mau, they are very active cats. He is likely attacking her because he wants something to do. Active play - fetch, fishing pole games, teaching him obedience commands, and then "tricks" - all will help use up his excess energy, and distract him from attacking her.

Lots of people who get Maus without doing proper research do not realize what an active, energetic breed they are.. and end up giving them up. Consider training him to walk on a leash so you can safely take him for a walk in the morning before you go to work, and in the evening before dinner - anything to help wear him out will help!

Also, in the wild, cats will attack and drive out sick members, as they can no longer hunt, so he may be sensing her illness ... so it's probably best to keep them separated while you are not home for now.