Net, you know she has these monthly episodes, so you need to figure out a way to deal with her and her moods during this time. Maybe do some research at the bookstore on effective coping skills.
You might also offer (AFTER HER PERIOD IS DONE!!) to go with her to see a Dr./OBGYN to see if there is something that can be done to help her. Tread carefully here, though! Be real careful!
And stop giving her ammunition. You say you want to establish trust then you get caught in a lie. Give her a reason to trust you and she will. Show by your actions that you can be trusted.
And remember trust takes on many forms. It is not just about telling the truth. If you say you are going to go to the store for your W to pick up some items and then you fail to do so, not only are you unreliable but you are also untrustworthy to fulfill your commitments.,
If you say you are going to remain calm during your W's monthly cycle and then allow yourself to get sucked into her misery, then you can't be trusted to remain neutral and avoid escalation.
See what I'm saying?
Me51 W53 S17 S14 M22 T25 Bomb-9/11; A-11/11; I move out 11/11
It's easy to find our bottom, it is our top that requires cultivation.
Every rough spot adds to our emotional constitution. -Barney Fife