Please don't wear yourself into the ground or you'll be no help to you or your mom or anyone else. Take care of YOU.
I've never heard of a 21-day Holter monitor, but that must be the latest thing. All of mine were only 24 hours, & that was enough of an annoyance. I also have CFS/FMS, so when I would get a "funny feeling" around my heart, it was not actually my heart but rather my blood pressure getting out of whack or my oxygen intake going wonky -- neither of which the Holter measured. I recall walking from the parking lot into the cardiologist's with the gizmo on, feeling unwell, & thinking "Great! At least this will surely show up!" I also figured the doc would catch something that was off at my appointment, but no luck there either. Some problems are just not straightforward & obvious, so that requires some creative thinking on the part of the medical team, which they're not always willing to do. You know, sometimes it really is zebras, not horses.