Apple Watch 4 ECG to weak

Hi,

My wife has an Apple Watch 4 and for some reason the Apple watch can't pick up her ECG, seems like the signal is too weak. When she uses my Apple Watch 4, the same. Always says "inconclusive". Is there a way to boos the IR signal that goes thru the skin? Seems like a waste of $ for this watch that can't detect a ECG signal,