I didn't get to see "Portrait of a Lady" but I have seen "The Piano" and studied the script (in hard copy.) Beautiful use of visuals (and indeed the musical sequences) as metaphorical dialogue. I would consider the piece a master class in the 'art' of film making as a visual medium, with some of the best unspoken dialogue outside of Sergio Leone.
Personally I would call it short of a 'great' movie as I'm not convinced the totality of the film lived up to the standard of its visuals. Holly Hunter and Sam Neill (in a difficult role) were superb but I thought Harvey Keitel was strangely flat. In a film where so much of the acting was deliberately underplayed, I thought Keitel sank into the scenery and for once his 'method' background didn't work for him.
What's your opinion of the film? (Also "Portrait of a Lady.")
(P/s If you have a chance to see her earlier (1989/90) work "Angel at my Table" - take it. Much of that piece (originally made - I believe- as a television miniseries then later released to cinema) is among Campion's finest work.