But recently it seems symptomatic of something deeper; she has seemed to rely on falsehood even when it's not been necessary.

Yes. That's what's bugging me; the lying isn't necessary.

But the compulsive lying is more symptomatic of something deeper--and I have a feeling that at some point it's going to come back and bite her badly.

It darn well better, or I will be very disappointed at the writers.
I just hope that she comes through it, survives it, learns and grows from it, becomes a better person. Otherwise, I'll be even more cross at the writers.