I love Lalla Ward as Romana, but Mary Tamm is definitely on the same level, seeing her break character here really emphasises just how different her performance was from how she was in real life, I find it very impressive.
If I had to pick my favourite Fourth Doctor season then its S16, and Romana I is easily my favourite companion of Tom's entire tenure. Its so clear that the were the greatest of friends and I only wish we got more time with Mary as the wonderfully glamorous ice queen. Its one of the reasons I'm so happy we got a full season of audio adventures with the two of them (Season 2, BigFinish Fourth Doctor Adventures). Wish we could have had even more adventures with the First Romana. A real gem. RIP Mary Tamm. Nearly a decade on from your sad passing, and your performances are still dazzling.