Welcome to HCM
I would like to ask you few questions like:-
-does she has loss of expression on that side?
-is she able to close her eye lid of that side completely?
-does this problem started after getting RCT started?
If all these symptoms are present then its a case of BELL'S PALSY
due to facial nerve
It might have happened because the anesthesia
given while starting RCT was probably given at wrong site i.e. somewhat in parotid capsule near facial nerve.
If that's the case you should concern oral & maxillofacial surgeon for getting it treated.