[justkate]

Maybe she was still impaired from partaking previously, even the night before?

Could be...

At this point, all assumptions in that regard seem equally valid.

I imagine toxicology could determine how long she had THC in her blood...but that's just another assumption.

[Lord_Baltar]

The tests for THC aren’t measured that way.

They test for trace in the blood.

However, trace from THC can remain in the system for around 30 days. Longer if they test hair.