Tracking cycle with IUD

Ok so full disclosure I'm a man whise married to a wonderful woman and the light of my life. I've started tracking her cycle through the Clue and eve apps with her permission. Not to predict when shell bleed since she has an IUD, but so I can better predict her moods, when I should have chocolate in the house etc. A perfect example of this is when she spirals emotionally and becomes depressed. It helps her to know that she's in a certain point in her cycle that would explain why she feels that way.

That all being said I've run into a big snag. It is nearly impossible for me to tell when a new cycle starts since she doesn't bleed. I got lucky once when she was spitting but aside from that I got nothing. Are their any other clear indicators of the beginning of a period cycle? Perhaps sore breasts or cramps?