Depressingly pedestrian I'm afraid. It could be an entry to a paint a Royal competition on a Saturday Morning TV show. Great portrait painters make an artistic statement as well as catching a likeness and this one is barely a likeness.
Rolf Harris would have done a better job - I bet he would have captured youthful vivacity rather then this seriously dull effort that completely fails to capture any hint of personality - she just looks drab. A good portrait reflects the sitter's personality.
Well, she certainly would have had before she married royalty! Her old passport photograph couldn't have made her look much worse than this offering...