I looked and Lord Harkon looks like a spritely young man, just like he's supposed to, but Serana looks like an old woman. Why is that?
I've noticed before that on every mod that adds and immortality trait some portraits stop ageing with it and other portraits continue ageing however neither die from old age, as far as I can tell it's a bug that strikes randomly though I might be incorrect.
I did the same a while back.For me Harkon Valerica and Serana all looked old. Then i added immortal=21 to seranas entry in the history files and all three of them look young now. weird.