So sorry to hear the bad news. As several have said, Luna doesn't know she's dying and will pick up on your sadness. Now is the time to show how much you love her, you will have lots of time to grieve later.
I am glad you have chosen not to put her through chemo etc., I am among the people who believe that the time gained with it and other treatments is often not quality time, unfortunately. I hope that Luna has a peaceful and painfree time and that you have many months left with her.
