For the record, I do plan on running Rosaria on one of my core Yun teams, as the secondary driver to Zhongli who even without atk speed buffs easily chews through 30 quota in around 6-7 seconds.
If there's ever a character like Chongyun but for Geo, on-field Yun Jin will become a legitimate strategy, by the way.
The main thing you actually want out of a partner for Yun is high normal attack multipliers.
Physical bonuses also tend to stack higher than elemental bonuses, allowing her single-slot multiplier to come closer to Yoimiya's than you might think.
Concluding that her potential is great, Yang Kai suggests that Ye Xi Yun supervise her training since she has the greatest cultivation experience on Shadowed Star.
Yang Yan determines that a friend of hers is particularly suited to teach her.