Sounds like she had auto brightness enabled, it can be quite dim depending on the environment. I always over ride it if I'm watching media.
Also, I just did a flight from USA (8 hrs) and watched back to back episodes and battery was nowhere near flat, above 60% if I remember correctly.
Maybe, specs wise it's not far off from the 500 nits max on the Pixel C. I'm guessing because it's OLED max brightness is probably not achievable with the brightness slider anyway, similar to the way the phones work.
Battery life I was surprised by, I can usually do 3-4 games of=f Vainglory on the Pixel C and only drop about 20-30% battery, that's about 1.5-2 hours screen on time, maybe it little longer if the games take a while.
The battery on the Tab 4 was below 40% from what I remember, not sure if it a combination of gaming and highish brightness but the battery life was disappointing, I don't know exactly what she started on but it was charged apparently.
I haven't even charged my Pixel C since, I haven't needed to, battery life is still fab after almost 3 years.
EDIT: The specs do somewhat explain that, 7300 vs 9240mAh