Ah ha! That’s actually a different question than the one that you asked, because those aren’t “modes” in the SmartThings system. They are “armed states.” The following thread explains the differences,
So good for @Navat604 for continuing to ask that question, because now we can get you the right answer.
The answer that I gave you above isn’t going to work, because that’s based on modes. there’s no smart lighting trigger for armed state change.
Right now, the only way to trigger based on the armed state changing is with custom code, including core. So to have a routine run when you change the SHM armed state on the dashboard, you’re really going to have to use core.
As you mentioned, it may be that just having a routine that itself changes the armed state ( along with whatever else you want done) and then setting up a widget for that routine will be the easiest for your wife to use. So you might want to look at that first, as it will be simpler to set up. You just create the routine that does everything you want, including changing the SHM armed state. So you might have a widget for a routine called “I’m home” and tapping that widget would disarm SHM and do whatever else you want the I’m home routine to do.
But if you do want to use The SHM armed state buttons on the SmartThings mobile app dashboard, you can do that with core, and there will be a lot of people to help you get it set up: