Not a rumor, but pure speculation! Jacqueline Durran was the costumer for both Little Women and Barbie, and it seems there's a decent possibility that she and Gerwig will team up again on Narnia.
I started thinking about this because I remember some of the criticism that the costumes in Gerwig's Little Women received about being too historically anachronistic. I can see the problem in a period piece, but historically anachronistic fashion would fit in just fine in Narnia! It's a mishmash of mythologies, cultures, time periods, and even worlds.
Besides her work on Gerwig's films, Jacqueline Durran has also worked on films such as Pride and Prejudice (2005), Atonement (2007), Anna Karenina (2012), Macbeth (2015), and Beauty and the Beast (2017).
That's not a bad shout. Looking at her résumé it does look like she tends to stick to a handful of the same directors over and over... About 5 or 6 Mike Leigh films on there, and probably just as many if not more Joe Wright films ... It stands to reason she would also continue with her run with Greta Gerwig as well.
Film wise it's a fantastic résumé, and in particular a lot of great movies with great period costume design - Peterloo, Cyrano, Spencer, 1917, Darkest Hour, Tinker Tailor... All highly rated by me
I guess though the one thing I'm not seeing on her resume is any truly out-and-out Fantasy design work, except for maybe Pan. It mostly tends to be films where she is designing costumes that look like existing real world clothing... even her Batman movie is the most grounded and down-to-earth of all the Batmans in terms of costume design and overall world building.
That's definitely not a negative though - all in all there probably aren't alot of movies in which a costume designer really has to create entire cultures, histories and worlds via costume design - but definitely something to consider.
@rose as long as she is historically accurate for the English characters, I'll be content. And modesty in the dressing of women and girls, or 'female' characters.
@icarus the only one in your list I've seen is Peterloo. It was very well done.
There, shining in the sunrise, larger than they had seen him before, shaking his mane (for it had apparently grown again) stood Aslan himself.
"...when a willing victim who had committed no treachery was killed in a traitor's stead, the Table would crack and Death itself would start working backwards."