YVR -- ?
LHR -- You are arriving / departing at the wonderful new fantastic Terminal 5 -- You can hit all the lounges inc the CR if you are also returing in F, you could also try for an Elemis Travel Spa session for your Mother for a complimentary massage treatment (Subject to availability)
I believe there are also a number of demi-beds where she could relax - think these are in the CR.