I've got you brother. My hand is firmly on your shoulder holding you away from that ledge.
One thing I've learned is don't do anything in anger in this situation. Examine the 'energy', or motivation, behind what you're thinking. If the energy is anger (and you're perfectly right and entitled to be angry mind you), then dont do anything except something to release that. Keep repeating the word 'calm' over and over and over. Chuck on some headphones and play your fave music at full tilt til your thoughts subside, or listen to some thought provoking podcasts. Have you tried Dr Robert Glover, author of NMMNG?
By all means, establish your boundaries about her cakeeating, but don't do it in a fit of anger. You're on the higher road, remember.
Keep your chin up mate
Cheers, DS
Me: early 40's XW: nearly 50 T: 15 M: 5 BD: Jan 19 S:10 SS: 22 SD: 24