She says its her third one but I don't know how she keeps getting bad units.
(although I do remember some guy going through eight Palm Pre replacements back in the thick of the early bad build quality days.)
Frankly, with a non-defective Pro 4, even taking normal wear-and-tear into account, I won't be able to even get its runtime DOWN to 45 minutes if I tried!
No idea what could be draining her battery so fast. Hopefully she didn't get some kind of bitcoin mining malware, that wouldn't be possible on Windows 10 S anyway.
What kind of software do you use? It must be something very demanding on resources (eg. battery life) or you're really running malware/virus. There's a chance that, unfortunately, you may have it on cloud or some USB and you download it to every device and you'd get a bad battery life on every single device, it wouldn't be SP4 related.