The use of the term "Wren" is illogical; the whole point of abolishing the WRNS as a separate service was so that women could do the same jobs as men in the Navy.
The most junior female ratings are still known as "Wrens" for historic reasons. But female officers in the Royal Navy are not. They wear the same gold sleeve lace as their male counterparts, rather than the old Wren blue stripes. And if Karen Pearce were still a Wren, she would be a First Officer. Not a Lieutenant Commander.