That's tricky, in that it depends on the version of watch she has. If she has the original or the Series 1 watch, it would only keep the heart rate/heart beat/calories burned/health info. Series 0 and 1 did not come with standalone GPS.
If it's Series 2 or later, the nice thing about the Apple Watch is that the non-cellular version is notably referred to as "GPS only". The GPS works independently, via satellite, without cellular connection. If it's a series 3 or 4, it can even mark elevation via onboard altimeter that works in tandem with the GPS.
However, the nice thing is, because she was wearing the watch throughout the duration, it tracked all of her health data. Heart rate. BPM. Active calories burned. So, worst-case scenario, you'll know exactly when her heart rate spikes, when she relaxes, when she is working hard, running/walking/sitting. With a Series 2 or later, you'll actually be able to follow her physical journey and map her along that entire route with when those peaks and valleys in her health data happen.
Also, it 100% knows if she's the person wearing it, so it will note this as an issue with the data. The watch knows this in order to not calculate a different person's health data alongside yours. It will track and record the health info anyhow, but will note it as an anomaly, and that info will be in the data LE receives.
Edited to add: When she arrived home, her watch connected to her WiFi and synced. If the battery was dead, it connected to WiFi and synced as soon as she began to charge it. There's no way that the watch still works and hasn't uploaded the data.
